`ims` document `OAuth2 Server-to-Server` support and associated `Workspace` Configurations

[francoisledroff]

With PR 166 we now have OAuth Support.
We still need however to document it.

• with updated README.md files in the core and ims modules
• with OAuth support built-in ims WorkspaceUtil and hence in our various *ServiceTester
• as well as in our docs at https://developer.adobe.com/events/docs/guides/api/

Related:

• aem aio-aem-events-publish: Service Account (JWT) DEPRECATED #155
• ims add a new OAuth2 Server-to-Server Request Interceptor #163

[francoisledroff]

the following associated PR #224 has been merged
consequently aio-lib-java version 2.0.0-SNAPSHOT has been released.
we will release a proper non snapshot version after a round of testing.