Maestro should notify repo owners if a subscription can't be executed due to a user error

[dkurepa]

Context

Recently we've seen some failed WorkItems in our logs that we're the result of incorrect repo configuration, not the fault of the service.
When this happens, ideally we wouldn't get a failed workitem, but the repo owners would be notified of it

Failure types

• Incorrect inclusion/exclusion filters in source-mappings: Source build reference packages main FF failing #6053
• Git file with mixed line endings, always appearing dirty: nuget-client FF fails while rebasing with dirty branch #6052
• Missing versioning files in the repo (eg: no global.json or Version.Details.xml)
• Subscription not updatable due to merge conflict in the existing PR itself (happens in version.details.xml)

[adamzip]

• Codeflow exceptions related to non-linear flows or failure to determine commit ancestry

Even if we don't have a well determined solution to that yet, we can still notify those failures so that repo owners know what happened