Changing fee recipient with KeyManager API does not trigger mev-boost relayer update without a restart

[nanexcool]

Describe the bug
Changing a validator's fee recipient address using the KeyManager API does not trigger an update with mev-boost relayers until the Nimbus client is restarted.

To Reproduce
Steps to reproduce the behavior:

1. Change fee recipient via KeyManager POST call
2. Confirm change via KeyManager GET call
3. Wait a couple of epochs and check relayers data for the validator
4. No change

Additional context
Smoothing Pools like Dappnode Smooth or Smoothly check that the validators have the correct fee recipient configured via mev-boost relayer lists. These for now (at least the fee recipient) are only updated when the Nimbus client is restarted.

[stonp89]

I experienced this bug as well

[tersec]

#6412