Identity package ref docs

[danieljurek]

Issues:

1. @azure/identity-cache-persistence and @azure/identity-vscode both do not link out to docs... though docs are being built. Somehow the ToC configuration is incorrect (could be related to overrides?)
   1. Check on status of latest packages and oonboard those versions and use -readme.md files from those tags
2. -readme.md files are linked under the Plugins section. This section is specified in a ToC override. This can be removed (if issue 1 is addressed) because the packages do pass.