Log fee recipients in VC (#3526)
Log fee recipients in VC (#3526)

## Issue Addressed

Resolves #3524 

## Proposed Changes

Log fee recipient in the `Validator exists in beacon chain` log. Logging in the BN already happens here https://github.com/sigp/lighthouse/blob/18c61a5e8be3e54226a86a69b96f8f4f7fd790e4/beacon_node/beacon_chain/src/beacon_chain.rs#L3858-L3865

I also think it's good practice to encourage users to set the fee recipient in the VC rather than the BN because of issues mentioned here https://github.com/sigp/lighthouse/issues/3432

Some example logs from prater:
```
Aug 30 03:47:09.922 INFO Validator exists in beacon chain        fee_recipient: 0xab97_ad88, validator_index: 213615, pubkey: 0xb542b69ba14ddbaf717ca1762ece63a4804c08d38a1aadf156ae718d1545942e86763a1604f5065d4faa550b7259d651, service: duties


Aug 30 03:48:05.505 INFO Validator exists in beacon chain        fee_recipient: Fee recipient for validator not set in validator_definitions.yml or provided with the `--suggested-fee-recipient flag`, validator_index: 210710, pubkey: 0xad5d67cc7f990590c7b3fa41d593c4cf12d9ead894be2311fbb3e5c733d8c1b909e9d47af60ea3480fb6b37946c35390, service: duties
```


Co-authored-by: Paul Hauner <a027184a55211cd23e3f3094f1fdc728df5e0500@paulhauner.com>

sigp/lighthouse,sigp/lighthouse,sigp/lighthouse,sigp/lighthouse