Moves the frontend generic configuration to a new plugin

[hbcarlos]

cc @davidbrochart

This PR moves the generic frontend configuration to a new plugin.

The idea is that another fps-base app could reuse the kernel plugin without depending on the fps-lab plugin, being able to implement a new frontend that reuses the kernel plugin.

[hbcarlos]

I believe the Check Release workflow is failing because of an unrelated issue. It is failing in the main branch too, and I think it is related to the order used to install the packages in the step check-python.

[davidbrochart]

Thanks Carlos!
The Check Release workflow is failing because we have not published fps-frontent to PyPI yet, so that's expected. I'll do it after merging this PR.
@blink1073 mentioned that jupyter-releaser should support local packages though, but I don't know if there's something to do to enable that?

[hbcarlos]

Thanks, @davidbrochart! I pushed a commit with the changes.

[blink1073]

local packages

It should already be doing that in check release, using a local pypi server, but that server only serves files that you've published.