Backport: Deprecate the kibana reserved user (#54967)

[legrego]

Backports #54967 to 7.x/7.8

[legrego]

@albertzaharovits why would this work on master, but not 7.x? They both appear to be using the same JDK 14...is there a different runtime target here where Map.of() isn't available?

https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+pull-request+oss-distro-docs/25732/console

15:14:22 > Task :x-pack:plugin:security:compileJava FAILED
15:14:22 /dev/shm/elastic+elasticsearch+pull-request+oss-distro-docs/x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/esnative/tool/SetupPasswordTool.java:72: error: cannot find symbol
15:14:22 public static final Map<String, String> USERS_WITH_SHARED_PASSWORDS = Map.of(KibanaSystemUser.NAME, KibanaUser.NAME);
15:14:22 ^
15:14:22 symbol: method of(String,String)
15:14:22 location: interface Map
15:14:22 Note: Some input files use or override a deprecated API.
15:14:22 Note: Recompile with -Xlint:deprecation for details.
15:14:22 Note: Some input files use unchecked or unsafe operations.
15:14:22 Note: Recompile with -Xlint:unchecked for details.
15:14:22 1 error

[elasticmachine]

Pinging @elastic/es-security (:Security/Authentication)

[albertzaharovits]

@albertzaharovits why would this work on master, but not 7.x? They both appear to be using the same JDK 14...is there a different runtime target here where Map.of() isn't available?

Yes, that's exactly right, the target runtime for the 7.x branch is probably JDK11 which is before the Map.of API has been introduced. This is a common issue we hit. You have to use Collections.unmodifiableMap in the 7.x backport.

Also, please don't forget to update the docs/reference/migration/migrate_7_8.asciidoc . It should mention the user (and role) which have been deprecated and will be removed in 8.