Update doc so it is clear that groups and tenants are resolved from the IdentityService

User story

As a java developer reading the documentation of:

AuthenticationProvider https://docs.camunda.org/javadoc/camunda-bpm-platform/7.3/org/camunda/bpm/engine/rest/security/auth/AuthenticationProvider.html|http://example.com/]

and

AuthenticationResult https://docs.camunda.org/javadoc/camunda-bpm-platform/7.3/org/camunda/bpm/engine/rest/security/auth/AuthenticationResult.html

it is clear to me that user groups and tenants are provided by the IdentityService.

Problem

• Confusion and unexpected behavior for users working with these APIs.
• It is not clear that groups and tenants do not have to be provided to these classes but rather will be provided by the IdentifyService further down the call chain.

AC

• The Javadoc of AuthenticationProvider and AuthenticationResult updated.
• From reading these doc pages, it is clear that groups and tenants are resolved via IdentityService.