feat(github-actions): remove preview label for non-googlers in pack-and-upload-artifact

[josephperrott]

This PR moves the automatic removal of the triggering preview label (e.g. `action: preview`) from `upload-artifacts-to-firebase` into the `pack-and-upload-artifact` action.

Key Changes:

1. Organized Label-Removal Logic: Added `remove-preview-label.ts` in `pack-and-upload-artifact/lib/` to check if the PR author is not a member of the `googlers` organization using the Angular Robot App's token and safely delete the triggering label.
2. Self-Contained Gating: Added `if: contains(github.event.pull_request.labels.*.name, inputs.triggering-label)` to all steps in `pack-and-upload-artifact/action.yml` so that the entire action is graceful and skips if the preview trigger label is not present on the PR.
3. Angular Robot Authentication: Performs all operations with the Angular Robot app token, avoiding the need for a custom GitHub Token passed as input.

[gemini-code-assist]

Code Review

This pull request introduces a new GitHub Action step to automatically remove the preview trigger label if the PR author is not a member of the googlers organization. The feedback highlights a critical authentication issue in the composite action due to unmapped inputs, and suggests optimizing the workflow by setting and checking a should-preview output to skip subsequent steps when appropriate. Additionally, improvements were suggested to handle potentially null PR authors, ensure robust token revocation in the finally block, and remove a redundant global cache.