Add back no-restricted-modules and no-restricted-imports ESLint rules

[oandregal]

They were removed in #6945 inadvertently.

[matticbot]

Test live: https://calypso.live/?branch=fix/eslint-add-back-no-restricted

[tyxla]

Nice, it's a good idea to have these added back.

However, I find something problematic here. If we set these as errors, we'll be forced to migrate away from sites-list in any file that currently includes it - which we can't do right now. Migration of sites-list still requires a lot of work, part of it has already been started and can be monitored in the dedicated project: https://github.com/Automattic/wp-calypso/projects/3

So, I'd recommend setting these to be warnings instead. Once we're able to safely get rid of sites-list, we can change these back to errors.

[oandregal]

The existing code that uses sites-list doesn't need to be migrated with this change, eslines will downgrade it to a warning for the CI/hooks not to complain.

My understanding is that we don't allow using those modules for any new code, that's where they'll be reported as errors. If that assumption holds false, we may set them as warnings or remove the rules - either way is fine with me, although I'd lean towards removing them.

[tyxla]

eslines will downgrade it to a warning for the CI/hooks not to complain.

Ah, I guess I should have got to know eslines better. Well, if that's the case, this LGTM 👍