Inactive validators: Allow consumer chains to disable non-provider-vals from validating

[p-offtermatt]

Problem

Some consumer chains may not want to be validated by validators that are outside of the hub active set.
We should give those chains the option to disable the feature, or restrict the potential validators to a smaller set (e.g. using the first 200 validators on the hub instead of all 500 bonded ones)

Closing criteria

We have implemented a way for consumer chains to not be validated by validators that are inactive on the hub.

Implementation

A possible implementation is to add a new param that allows consumers to filter the potential validator set to the first N validators. Ultimately, the need is that consumer chains want to be able to set a floor on "quality" of validators allowed to validate the chain, which includes the stake/rank they have on the hub.