[Release/CI] Github flow to build `polkadot`/`polkadot-parachain` rc binaries...

[Release/CI] Github flow to build `polkadot`/`polkadot-parachain` rc binaries and deb package (#5963)

This PR introduces a GitHub flow, that should replace a semi manual part
of the release process to build rc binaries for `polkadot` and
`polkadot-parachain` + the `polkadot` deb package.

Right now, this part of the release is done on the `cleanroom` machine
by the release engineers via triggering bash scripts directly on the
server. These GitHub flows should replace it and move everything to the
CI.

The whole flow is meant to be run in the new
[paritytech-release](https://github.com/paritytech-release) where the
automated release is going to be moved.

The flow includes the following steps:
- Build `polkadot`, `polakdot-prepare-worker`, `polkadot-execute-worker`
and `polkadopt-parachain` binaries
- Sign those artefacts using `gpg` and generate a sha256 checksum
- Build deb package for `polakdot`
- Make a GitHub attestation
- Upload artefacts to the S3 buckets

Closes: https://github.com/paritytech/release-engineering/issues/223

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Co-authored-by: Oliver Tale-Yazdi <[email protected]>