Update releasing configuration

Adds few changes:

1. Puts all release jobs in the build stage (currently beta is released at the same stage when linting and validation is executed, so... 😉)
2. Adds an environment name to the stable job (it was missing).
3. Clears the environment name of the beta job (there is no need to add the reference there, it's definitely not expected; there should be one beta, always the latest one).
4. Drops the SHA part from the beta image name (as described at #3 (closed)).

Closes #3 (closed)