allow admins to update validator set

[redshiftzero]

We should have an easy path for validators to join the network without requiring creating a new genesis file with them added.

One could do this by adding a validators field to the Config struct in felidae.

To add (or remove) a validator, admins would coordinate to add an entry to the list in the validators field.

That would be passed to CometBFT in EndBlock (or FinalizeBlock in 0.38).

We would also need to keep that config in sync with any changes that occur due to tombstoning (#32).