Add a simple config backed section storage plugin

Vivek Panicker → made their first commit to this issue’s fork.

1. Don't think the ID should remain test_simple_config
2. Shouldn't this be marked @internal now?
3. buildRoutes() is return test routes
4. Config name is also still using test.

@smustgrave Except for point 2, I have fixed the rest.
Not sure what to do about point 2.
So leaving this issue in the same state.

This might need more guidance from @larowlan on his intentions.