Add documentation for the new 5.2 version in main branch.

Original Pull Request #2552
Closes #2551

Author: sothawo

src/main/asciidoc/preface.adoc

@@ -37,6 +37,7 @@ built and tested.
 [cols="^,^,^,^,^",options="header"]
 |===
 | Spring Data Release Train | Spring Data Elasticsearch | Elasticsearch | Spring Framework | Spring Boot
+| 2023.1 (?) | 5.2.x | 8.7.1 | 6.0.x | 3.1.x
 | 2023.0 (Ullmann) | 5.1.x | 8.7.0 | 6.0.x | 3.1.x
 | 2022.0 (Turing) | 5.0.x | 8.5.3 | 6.0.x | 3.0.x
 | 2021.2 (Raj) | 4.4.xfootnote:oom[Out of maintenance] | 7.17.3 | 5.3.x | 2.7.x

src/main/asciidoc/reference/elasticsearch-migration-guide-5.1-5.2.adoc

@@ -0,0 +1,11 @@
+[[elasticsearch-migration-guide-5.1-5.2]]
+= Upgrading from 5.1.x to 5.2.x
+
+This section describes breaking changes from version 5.1.x to 5.2.x and how removed features can be replaced by new introduced features.
+
+[[elasticsearch-migration-guide-5.1-5.2.breaking-changes]]
+== Breaking Changes
+
+
+[[elasticsearch-migration-guide-5.1-5.2.deprecations]]
+== Deprecations

src/main/asciidoc/reference/elasticsearch-new.adoc

@@ -1,6 +1,9 @@
 [[new-features]]
 = What's new
 
+[[new-features.5-2-0]]
+== New in Spring Data Elasticsearch 5.2
+
 [[new-features.5-1-0]]
 == New in Spring Data Elasticsearch 5.1
 

src/main/asciidoc/reference/migration-guides.adoc

@@ -15,4 +15,8 @@ include::elasticsearch-migration-guide-4.3-4.4.adoc[]
 
 include::elasticsearch-migration-guide-4.4-5.0.adoc[]
 
+include::elasticsearch-migration-guide-5.0-5.1.adoc[]
+
+include::elasticsearch-migration-guide-5.1-5.2.adoc[]
+
 :leveloffset: -1