Removal Post for OAuth Tokens Without An Expiration

Via #21745 (closed) we added default expiration of OAuth tokens for new OAuth Applications, and an option to enable it for existing applications. In %15.0 we can remove the backward compatibility and force all tokens to expire within 2 hours.

This issue is to create the removal post to announce the removal in %15.0 #340848 (closed)

In 15.0 we will set an expiry for every existing token. If an external integration doesn't support expiring tokens then the integration will stop working upon upgrade.