[API] - Add Logic to ImpactedFiles Filtering by Flag to Indicate Proper States

[nicholas-codecov]

We recently added the functionality to filter impacted files by flags, but didn't catch all the scenarios. We want to catch the scenario when a flag doesn't belong to the list of flags you can filter by similar to how we do it here https://github.com/codecov/codecov-api/blob/main/graphql_api/types/commit/commit.py#L176.

This might need a bit of refactoring of the impactedFiles resolver, as we currently don't return a custom ImpactedFiles type along different errors the way pathContents does. For this change, we'll likely want to:

• Create a union type similar to how pathcontents does as seen here https://github.com/codecov/codecov-api/blob/main/graphql_api/types/path_contents/path_content.graphql#L36 with at least a ImpactedFiles and UnknownFlags result
• Refactor the impactedFiles resolver to enable surfacing the UnknownFlags exception early on
  • We'll likely have to create a new resolver, impactedFilesTemp or something along the lines, so the frontend doesn't break with these changes
• I believe that's it. Let me know (@adrian-codecov) if you have any qs

[JerrySentry]

impactedFiles(filters: $filters) {
__typename
... on ImpactedFiles {
results {
# [ImpactedFile]
}
}
... on UnknownFlags {
message
}
}