chore: add combine-dependabot-prs workflow

[pownkel]

Details

Add a new workflow to automatically combine dependabot PRs into a single PR. Any PR with a failing build or the pr: do not combine label will be excluded from the new combined PR.

This workflow runs automatically every Monday at 1PM UTC (6AM PST), or it can be run manually from the "actions" tab in the repo.

Motivation

Reduce the number of dependabot commits in the repo

Context

This action is already used in the accessibility-insights-service repo on a manual trigger. After a discussion, our team has decided to experiment with using this action on an automatic trigger in our other repos.

Pull request checklist

• [n/a] Addresses an existing issue: #0000
• [n/a] Ran yarn null:autoadd
• [n/a] Ran yarn fastpass
• [n/a] Added/updated relevant unit test(s) (and ran yarn test)
• [n/a] Verified code coverage for the changes made. Check coverage report at: <rootDir>/test-results/unit/coverage
• PR title AND final merge commit title both start with a semantic tag (fix:, chore:, feat(feature-name):, refactor:). See CONTRIBUTING.md.
• [n/a] (UI changes only) Added screenshots/GIFs to description above
• [n/a] (UI changes only) Verified usability with NVDA/JAWS