Fixes #3608

From the "sync cloud integrations" process we were setting "create if needed", which in fetchOrCreateSession will cause the gkdev connect flow to start (and website to open) if the session could not be fetched from the cloud.

This causes undesirable/unexpected UX for users, especially because it can happen from the background sync for cloud integrations, and can occur daily on each check-in.

In the case of #3608, the user had no local gitlab session, one existed in the cloud, but it was expired and could not be refreshed, causing the prompt to happen regularly on vscode launch or profile change.

This change adds a new sync flag to the ensureSession/getSession auth flow that acts as a softer version of createIfNeeded, and will not trigger a connectCloudIntegration call in fetchOrCreateSession of CloudIntegrationAuthenticationProvider if session was returned as undefined from fetchSession, either due to an error or because it didn't exist, since sync, unlike createIfNeeded, does not satisfy the shouldCreateSession check.