Map OIDC groups to Orgs/Teams (#21441)

Fixes #19555

Test-Instructions:
https://github.com/go-gitea/gitea/pull/21441#issuecomment-1419438000

This PR implements the mapping of user groups provided by OIDC providers
to orgs teams in Gitea. The main part is a refactoring of the existing
LDAP code to make it usable from different providers.

Refactorings:
- Moved the router auth code from module to service because of import
cycles
- Changed some model methods to take a `Context` parameter
- Moved the mapping code from LDAP to a common location

I've tested it with Keycloak but other providers should work too. The
JSON mapping format is the same as for LDAP.


![grafik](https://user-images.githubusercontent.com/1666336/195634392-3fc540fc-b229-4649-99ac-91ae8e19df2d.png)

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/admin/auths.go

@@ -204,6 +204,8 @@ func parseOAuth2Config(form forms.AuthenticationForm) *oauth2.Source {
 		GroupClaimName:                form.Oauth2GroupClaimName,
 		RestrictedGroup:               form.Oauth2RestrictedGroup,
 		AdminGroup:                    form.Oauth2AdminGroup,
+		GroupTeamMap:                  form.Oauth2GroupTeamMap,
+		GroupTeamMapRemoval:           form.Oauth2GroupTeamMapRemoval,
 	}
 }