Add the possibility to log in with XWiki authentication service

[ChiuchiuSorin]

Currently, the interface that provides the option to log in with either XWiki or Microsoft Azure is generated by Identity OAuth application, but this will be removed after the OIDC integration. Currently, OIDC does not provide the option to select the standard authenticator at login, unless an additional parameter is added to the login URL (http://localhost:8080/xwiki/bin/login/XWiki/XWikiLogin?oidc.skipped=true).

A possible workaround would be to create a Drawer Header Item extension point to add an additional login option for using the XWiki authenticator. In this case, a new Azure configuration class should be added to provide the option for the admins to display or not the additional login option.

[snazare]

from Thomas: to look at REST use case: an alternative to BASIC is now to use tokens, in which case you don't need to skip OIDC as long as you have a token in the request (the token is checked first).