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/auth/linkaccount.go

@@ -16,6 +16,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/web"
 	auth_service "code.gitea.io/gitea/services/auth"
+	"code.gitea.io/gitea/services/auth/source/oauth2"
 	"code.gitea.io/gitea/services/externalaccount"
 	"code.gitea.io/gitea/services/forms"
 
@@ -267,5 +268,11 @@ func LinkAccountPostRegister(ctx *context.Context) {
 		return
 	}
 
+	source := authSource.Cfg.(*oauth2.Source)
+	if err := syncGroupsToTeams(ctx, source, &gothUser, u); err != nil {
+		ctx.ServerError("SyncGroupsToTeams", err)
+		return
+	}
+
 	handleSignIn(ctx, u, false)
 }