Adapt brain to Rocket Pool package

[dsimog01]

In order to fit the needs of the new Rocket Pool Package, we need to perform the following changes:

1. The fee recipient for RP validators should not be overridden in the brain, it should keep the one that is sent by the RP package (should we check it is actually that package the one sending the keystores?)
2. The user should not be able to change the fee recipient from the brain (already done)
3. The RP package should be able to change the fee recipient for a certain validator. We have two options for this:
   a. Allow the RP package to change the fee recipient by calling the updateValidators() function
   b. Allow the RP package to remove the keystores and upload them again with the new value for the fee recipient

[pablomendezroyo]

Sounds good!

The point that requires more development is 3. I would implement an API that would allow changing fee recipients in the brain database (which then will be persisted by the cron in the brain). I would also set this API endpoint to only edit Rocketpool fee recipients

My concerns are exposing this endpoint to the docker network, so any package would be allowed to do requests. Maybe a Host: rocketpool-goerli.dappnode would be a good start

[ujavid]

Would any solutions mentioned here solve this problem?:
#243