[Task] Add Action automation to prevent dependency update merges until reviewer removes label

[andrewazores]

    We can probably build some further automation too, like having Dependabot apply a `needs-downstream-check` label and an Action that blocks merge until that label is removed.

Originally posted by @andrewazores in https://github.com/cryostatio/cryostat/issues/1181#issuecomment-1304211625

[maxcao13]

Does needs-triage fit the solution? If not, I will disallow github-actions to apply the label when dependabot creates a pull request.