[MM-47384] Make OpenID Connect free for all (#21556)

* wip: make OpenID Connect free-for-all

* Deprecation note: GoogleOAuth, Office365OAuth

* Improve deprecation comments

Co-authored-by: Martin Kraft <martin@upspin.org>

* Lint fix

* Add model/oauthproviders, move google, openid, office365 from enterprise

* Vet fixes

* Remove redundant log

Co-authored-by: Martin Kraft <martin@upspin.org>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

cmd/mattermost/main.go

@@ -10,7 +10,11 @@ import (
 	// Import and register app layer slash commands
 	_ "github.com/mattermost/mattermost-server/v6/app/slashcommands"
 	// Plugins
-	_ "github.com/mattermost/mattermost-server/v6/model/gitlab"
+	_ "github.com/mattermost/mattermost-server/v6/model/oauthproviders/gitlab"
+	_ "github.com/mattermost/mattermost-server/v6/model/oauthproviders/google"
+	_ "github.com/mattermost/mattermost-server/v6/model/oauthproviders/office365"
+	_ "github.com/mattermost/mattermost-server/v6/model/oauthproviders/openid"
+
 	// Enterprise Imports
 	_ "github.com/mattermost/mattermost-server/v6/imports"
 )