Introduced high-level abstractions for targetable requests in general.
- PUS Service 3 (HK) abstraction for targetable HK requests
- PUS Service 8 (Action) abstraction for targetable action requests
- Add new shared subcrate satrs-shared to split off some shared
components not expected to change very often.
- Renmame `satrs-core` to `satrs`. It is expected that sat-rs will remain
the primary crate, so the core information is superfluous, and core also
implies stability, which will not be the case for some time.
