docker-dev: Use loader-package implems from swh.loader.core modules
This also removes the potential [1] breaking of the different services (referencing the old task names without the module installed)
- [1] I did not see it in the earlier diff (!112 (closed)).
I also did not yet tested it entirely (in-progress, that should not prevent from merging as it stabilizes a bit more already).
Now swh-loader image starts.
Related T1389
Migrated from D2305 (view on Phabricator)