[Release|CI/CD] Add pipeline to promote release candidate from rcX to final in S3 (#6748)

This PR adds the pipeline, that moves release candidate artefacts from
`polkadot-stableYYMM-rcX` bucket to the one that is going to be the
final `polkadot-stableYYMM` (bucket name matches the tag name). So that
it could be used for publishing later without a need to re-build it
again.