[skdman] Separation of concerns between packager and announcer

[aalmiray]

The packager should only perform the following commands: release, release + default.
The announcer should only perform: announce.

Currently the packager supports these commands:

• major: release + default + announce
• minor: release + announce

The packager allows multiple candidates per project while the announcer allows a single one.

This change would require:

• both packager and announcer be configured at the same time. currently they are mutually exclusive.
• the announcer to collect all candidates configured per distribution and perform a release for each one.
• if no packagers are configured then the announcer performs the same behavior it does right now: single candidate per project, with the choice of major or minor release.

Discussed with @maxandersen