Introduce a fallback error message for GitLab Duo in the IDE

Problem to solve

Starting with gitlab-vscode-extension!1391 (merged) we surface an error in IDEs that says:

Code Suggestions is now a paid feature, part of Duo Pro. Contact your GitLab administrator to upgrade

This message is internally backed by this "license check" which can make it a misnomer in some cases. Checking the license is just one small part of this since this check, which calls this GraphQL query, which in return checks a backend policy via current_user.can?(:access_code_suggestions) here.

This misleading message is confusing for both customers and our team when troubleshooting.

Proposal

For now, use a generic error message instead of suggestion that there is a problem with paid subscription until the failure reasons can be mapped to specific UI copy.

Code Suggestions is now a paid feature, part of Duo Pro. Contact your GitLab administrator to upgrade

{Something went wrong} Tentative to change see thread #476579 (comment 2067440907)