Add chain-spec-builder docker image (#4655)
This PR adds possibility to publish container images for the `chain-spec-builder` binary on the regular basis. Related to: https://github.com/paritytech/release-engineering/issues/190
This PR adds possibility to publish container images for the `chain-spec-builder` binary on the regular basis. Related to: https://github.com/paritytech/release-engineering/issues/190