[API] Refactors namespace and requiring API code

Based on the code written in the Elasticsearch Serverless client, this change makes the creation of
the namespace clients dynamic, removing all the files that were under `namespace` before.

Some outdated and deprecated code was removed too, like unnecessary namespaces.

Author: picandocodigo

elasticsearch-api/lib/elasticsearch/api.rb

@@ -15,79 +15,102 @@
 # specific language governing permissions and limitations
 # under the License.
 
-require "cgi"
-require "multi_json"
-
-require "elasticsearch/api/version"
-require "elasticsearch/api/namespace/common"
-require "elasticsearch/api/utils"
+require 'cgi'
+require 'multi_json'
+require 'elasticsearch/api/version'
+require 'elasticsearch/api/utils'
 require 'elasticsearch/api/response'
 
-Dir[ File.expand_path('../api/actions/**/*.rb', __FILE__) ].each   { |f| require f }
-Dir[ File.expand_path('../api/namespace/**/*.rb', __FILE__) ].each { |f| require f }
+Dir[File.expand_path('api/actions/**/*.rb', __dir__)].each { |f| require f }
 
 module Elasticsearch
   # This is the main module for including all API endpoint functions
   # It includes the namespace modules from ./api/actions
   module API
+    include Elasticsearch::API::Actions
     DEFAULT_SERIALIZER = MultiJson
 
     HTTP_GET          = 'GET'.freeze
     HTTP_HEAD         = 'HEAD'.freeze
     HTTP_POST         = 'POST'.freeze
     HTTP_PUT          = 'PUT'.freeze
     HTTP_DELETE       = 'DELETE'.freeze
-    UNDERSCORE_SEARCH = '_search'.freeze
-    UNDERSCORE_ALL    = '_all'.freeze
-    DEFAULT_DOC       = '_doc'.freeze
 
-    # Auto-include all namespaces in the receiver
+    module CommonClient
+      attr_reader :client
+
+      def initialize(client)
+        @client = client
+      end
+
+      def perform_request(method, path, params = {}, body = nil, headers = nil, request_opts = {})
+        client.perform_request(method, path, params, body, headers, request_opts)
+      end
+    end
+
+    # Add new namespaces to this constant
     #
-    def self.included(base)
-      base.send :include,
-                Elasticsearch::API::Common,
-                Elasticsearch::API::Actions,
-                Elasticsearch::API::Cluster,
-                Elasticsearch::API::Nodes,
-                Elasticsearch::API::Indices,
-                Elasticsearch::API::Ingest,
-                Elasticsearch::API::Snapshot,
-                Elasticsearch::API::Tasks,
-                Elasticsearch::API::Cat,
-                Elasticsearch::API::Remote,
-                Elasticsearch::API::DanglingIndices,
-                Elasticsearch::API::Features,
-                Elasticsearch::API::AsyncSearch,
-                Elasticsearch::API::Autoscaling,
-                Elasticsearch::API::CrossClusterReplication,
-                Elasticsearch::API::DataFrameTransformDeprecated,
-                Elasticsearch::API::Enrich,
-                Elasticsearch::API::Eql,
-                Elasticsearch::API::Fleet,
-                Elasticsearch::API::Graph,
-                Elasticsearch::API::IndexLifecycleManagement,
-                Elasticsearch::API::License,
-                Elasticsearch::API::Logstash,
-                Elasticsearch::API::Migration,
-                Elasticsearch::API::MachineLearning,
-                Elasticsearch::API::SearchableSnapshots,
-                Elasticsearch::API::Security,
-                Elasticsearch::API::SnapshotLifecycleManagement,
-                Elasticsearch::API::SQL,
-                Elasticsearch::API::SSL,
-                Elasticsearch::API::TextStructure,
-                Elasticsearch::API::Transform,
-                Elasticsearch::API::Watcher,
-                Elasticsearch::API::XPack,
-                Elasticsearch::API::SearchApplication,
-                Elasticsearch::API::Synonyms,
-                Elasticsearch::API::Esql,
-                Elasticsearch::API::Inference,
-                Elasticsearch::API::Simulate,
-                Elasticsearch::API::Connector,
-                Elasticsearch::API::QueryRules
+    API_NAMESPACES = [:async_search,
+                      :cat,
+                      :cross_cluster_replication,
+                      :cluster,
+                      :connector,
+                      :dangling_indices,
+                      :enrich,
+                      :eql,
+                      :esql,
+                      :features,
+                      :fleet,
+                      :graph,
+                      :index_lifecycle_management,
+                      :indices,
+                      :inference,
+                      :ingest,
+                      :license,
+                      :logstash,
+                      :migration,
+                      :machine_learning,
+                      :nodes,
+                      :query_rules,
+                      :search_application,
+                      :searchable_snapshots,
+                      :security,
+                      :simulate,
+                      :snapshot_lifecycle_management,
+                      :snapshot,
+                      :sql,
+                      :ssl,
+                      :synonyms,
+                      :tasks,
+                      :text_structure,
+                      :transform,
+                      :watcher,
+                      :xpack].freeze
+
+    UPPERCASE_APIS = ['sql', 'ssl'].freeze
+    API_NAMESPACES.each do |namespace|
+      name = namespace.to_s
+      module_name = if UPPERCASE_APIS.include?(name)
+                      name.upcase
+                    elsif name == 'xpack'
+                      'XPack'
+                    else
+                      name.split('_').map(&:capitalize).join
+                    end
+      class_name = "#{module_name}Client"
+
+      klass = Class.new(Object) do
+        include CommonClient, Object.const_get("Elasticsearch::API::#{module_name}::Actions")
+      end
+      Object.const_set(class_name, klass)
+      define_method(name) do
+        instance_variable_set("@#{name}", klass.new(self))
+      end
     end
 
+    alias ml machine_learning
+    alias ilm index_lifecycle_management
+
     # The serializer class
     #
     def self.serializer