Investigate stable and nightly release channels in combination with self-update

[simonsan]

Investigate possibilities to create stable and nightly release channels in combination with self-update command. Would probably involve some settings that need to be made persistent in RUSTIC_HOME, to be able to switch release channels.

Currently also blocked by our CI/CD workflows, especially the release one. So we publish the same (signed) packages/artifacts (WRT what they contain, e.g. configs, man page, etc.) for stable and nightly, so we can switch between them seemlessly.

Although we need to be wary in the future for breaking changes between nightly and stable, where it could be not as easy to downgrade again. In the best case scenario, we design new features:

• in a backwards-compatible manner (until a certain point)
• rather additive
• work with editions or other versioning schemes

Especially breaking changes in the config will be rather painful. So we need to think about a good way to deal with that.