[CI] Fix Release CI

[pandres95]

As of now, the Release CI action produces some artifacts (runtime WASM and the now deprecated virto-node) and a Docker image that exposes the virto-node.

This process should change to build chain-spec-generator instead and output a Docker image that extends from parity/polkadot-parachain and uses chain-spec-generator to produce the aforementioned chainspec (or store it somewhere in the image).

This is to preserve some degree of compatibility, but it's expected that collators/nodes migrate to a pure implementation of polkadot-parachain.