GET `/eth/v1/validator/{pubkey}/feerecipient` of an existing remotekey returns 404
**Describe the bug**

After successfully [POST remotekey](https://ethereum.github.io/keymanager-APIs/#/Remote%20Key%20Manager/importRemoteKeys) through **validator keymanager API**, the [GET request of the feeRecipient](https://ethereum.github.io/keymanager-APIs/#/Fee%20Recipient/listFeeRecipient) for such remotekey returns 404, "validator not found"

**Expected behaviour**

Return the feeRecipient that the validator will use when proposing a block. Even if the Fee recipient has not been set through keymanager API, it must return the one that will use. In this case, this is the one set through the flag `--suggested-fee-recipient`.

**To Reproduce**
Steps to reproduce the behavior:
1. Platform details (OS, architecture):  running nimbus as **multiservice**  with docker.
2. Branch/commit used: nimbus version 25.1.0
3. Commands being executed: POST and GET fee recipient endpoints. See https://ethereum.github.io/keymanager-APIs/#/Fee%20Recipient
4. Relevant log lines: 404, "validator not found"

**Additional context**
Running nimbus in dappnode. See https://github.com/dappnode/DAppNodePackage-nimbus-generic