[Feature] Handle error and error_description more gracefully with denied via an Authorization Policy

I have searched the existing feature requests, both open and closed, to make sure this is not a duplicate request. • Yes The feature This feature request is about changing how Immich's web client handles an access_denied from an IdP. Ideally Immich would match the [OAuth 2.0 Auth RFC6749] compliant error response "access_denied" and provide a concise string of its own, something like "Unauthorized" as opposed to the current text: "Failed to finish oauth" Longer version: When configuring Authelia in such a way that it can deny a logged in user access to Immich, e.g. via a Authorization Policy, for users who are logged in but not allowed to access immich it returns them to immich with a URL like the following: The parameters from the URL: error: "access_denied" error_description: "The resource owner or authorization server denied the request. The user was denied access to this client." Immich's Web U…