Make it possible to mark module as "visible" for users

[pstibrany]

Not all modules should be selectable as "targets", only user-visible ones. For example, selecting "api" or "memberlist-kv" as targets makes no sense (and actually selecting "memberlist-kv" leads to panic, since this module doesn't depend on anything, but Cortex.Run method still tries to register some routes to API -- which is not initialized).

Once we have ability to set some modules as user-visible, InitModuleServices should report available modules if incorrect module name is passed to it.

/cc @annanay25

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 60 days. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.

[pstibrany]

Implemented in #2752.