config: Clarify the configuration setup path for the server part
Mixin SWHConfig is deprecated. This unplugs the inheritance to it (too much complexity for no good reason).
Feel free to propose something better. My plan is to currently unplug this everywhere where it's left and then remove that SWHConfig mixin [1]
Related to swh-core#1532 (closed)
Test Plan
tox
Migrated from D3953 (view on Phabricator)