Proposed change for disabling prometheus internal

[thunderthome]

I've made a pull request for you guys to make sure that the prometheus internal enabled works and doesn't just become the default fallback value.
#222

[github-actions]

This issue has been marked as stale because it has been open for 180 days with no activity. Please remove the stale label or comment or this issue will be closed in 5 days.

[markgloyne]

Hi, This is still an issue which renders enabling Thanos via the internal section unusable.

The PR mentioned above which is now closed due to becoming stale should fix the issue.