Add generator paths to mergeable labels

[kpumuk]

Currently we don't tag language-specific generator files with the respective language label on GitHub. This PR corrects it.

In addition to that, root-level package files (like ApacheThrift.nuspec and go.mod) are now labeled too.

• Did you create an Apache Jira ticket? (Request account here, not required for trivial changes)
• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
• Did you squash your changes to a single commit? (not required, but preferred)
• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
• If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources.