mw/log: dynamically loadable backend support

### Product Increment Description

`@score_baselibs//mw/log` to serve as the sole logging target. The integrator will be responsible for making the required backends available for each target platform, and `mw/log` will take care of loading them dynamically as shared libraries (.so)

### Acceptance Criteria (DoD)

Existing functionality unaffected
Existing Users unaffected
No regressions introduced.
NO public API breakage