Replace peter-evans/dockerhub-description and snok/container-retention-policy with first-party alternatives

[Copilot]

Eliminates two third-party GitHub Actions dependencies by reimplementing their functionality directly using the Docker Hub REST API and GitHub's gh CLI.

push-container-images.yml — peter-evans/dockerhub-description

Replaced with a PowerShell run step (consistent with the job's existing shell: pwsh default) that authenticates via POST /v2/users/login and updates the repo description via PATCH /v2/repositories/{repo}/. Secrets are passed through env vars rather than inline interpolation.

clean-ghcr.yml — snok/container-retention-policy

Replaced with a bash run step using gh CLI and jq (both pre-installed on ubuntu-latest) against the GitHub Packages API. Paginates all versions, filters by tag pattern (pr-* / *-alpha.*) and a 2-week updated_at cutoff, then bulk-deletes matches. Added explicit packages: write permission to the job.

gh api --paginate "/orgs/particular/packages/container/servicecontrol-masstransit-connector/versions" \
  | jq -r --arg cutoff "$CUTOFF" '
      .[]
      | select(
          (.metadata.container.tags | map(test("^pr-") or test("-alpha\\.")) | any) and
          (.updated_at < $cutoff)
        )
      | .id' \
  | while IFS= read -r version_id; do
      gh api --method DELETE ".../versions/$version_id"
    done