Document possible values of analytics command (#15039)

* docs: add possible values to ref doc for analytics command

* docs: add ci value

Author: jbogarthyde

packages/angular/cli/commands/analytics-long.md

@@ -0,0 +1,7 @@
+The value of *settingOrProject* is one of the following.
+* "on" : Enables analytics gathering and reporting for the user.
+* "off" : Disables analytics gathering and reporting for the user.
+* "ci" : Enables analytics and configures reporting for use with Continuous Integration,
+which uses a common CI user.
+* "prompt" : Prompts the user to set the status interactively.
+* "project" : Sets the default status for the project to the *projectSetting* value, which can be any of the other values. The *projectSetting* argument is ignored for all other values of *settingOrProject*.

packages/angular/cli/commands/analytics.json

@@ -2,7 +2,7 @@
   "$schema": "http://json-schema.org/schema",
   "$id": "ng-cli://commands/analytics.json",
   "description": "Configures the gathering of Angular CLI usage metrics. See https://v8.angular.io/cli/usage-analytics-gathering.",
-  "$longDescription": "",
+  "$longDescription": "./analytics-long.md",
 
   "$aliases": [],
   "$scope": "all",