Allow per validator fee recipient via flag or file in validator client (similar to graffiti / graffiti-file) (#2924)

## Issue Addressed

#2883 

## Proposed Changes

* Added `suggested-fee-recipient` & `suggested-fee-recipient-file` flags to validator client (similar to graffiti / graffiti-file implementation).
* Added proposer preparation service to VC, which sends the fee-recipient of all known validators to the BN via [/eth/v1/validator/prepare_beacon_proposer](https://github.com/ethereum/beacon-APIs/pull/178) api once per slot
* Added [/eth/v1/validator/prepare_beacon_proposer](https://github.com/ethereum/beacon-APIs/pull/178) api endpoint and preparation data caching
* Added cleanup routine to remove cached proposer preparations when not updated for 2 epochs

## Additional Info

Changed the Implementation following the discussion in #2883.



Co-authored-by: pk910 <philipp@pk910.de>
Co-authored-by: Paul Hauner <paul@paulhauner.com>
Co-authored-by: Philipp K <philipp@pk910.de>

validator_client/src/http_api/create_validator.rs

@@ -139,6 +139,7 @@ pub async fn create_validators_mnemonic<P: AsRef<Path>, T: 'static + SlotClock,
                 voting_password_string,
                 request.enable,
                 request.graffiti.clone(),
+                request.suggested_fee_recipient,
             )
             .await
             .map_err(|e| {
@@ -152,6 +153,7 @@ pub async fn create_validators_mnemonic<P: AsRef<Path>, T: 'static + SlotClock,
             enabled: request.enable,
             description: request.description.clone(),
             graffiti: request.graffiti.clone(),
+            suggested_fee_recipient: request.suggested_fee_recipient,
             voting_pubkey,
             eth1_deposit_tx_data: eth2_serde_utils::hex::encode(&eth1_deposit_data.rlp),
             deposit_gwei: request.deposit_gwei,
@@ -170,6 +172,7 @@ pub async fn create_validators_web3signer<T: 'static + SlotClock, E: EthSpec>(
             enabled: request.enable,
             voting_public_key: request.voting_public_key.clone(),
             graffiti: request.graffiti.clone(),
+            suggested_fee_recipient: request.suggested_fee_recipient,
             description: request.description.clone(),
             signing_definition: SigningDefinition::Web3Signer {
                 url: request.url.clone(),

validator_client/src/http_api/keystores.rs

@@ -201,6 +201,7 @@ fn import_single_keystore<T: SlotClock + 'static, E: EthSpec>(
             password,
             true,
             None,
+            None,
         ))
         .map_err(|e| format!("failed to initialize validator: {:?}", e))?;
 

validator_client/src/http_api/mod.rs

@@ -409,6 +409,7 @@ pub fn serve<T: 'static + SlotClock + Clone, E: EthSpec>(
                     drop(validator_dir);
                     let voting_password = body.password.clone();
                     let graffiti = body.graffiti.clone();
+                    let suggested_fee_recipient = body.suggested_fee_recipient;
 
                     let validator_def = {
                         if let Some(runtime) = runtime.upgrade() {
@@ -418,6 +419,7 @@ pub fn serve<T: 'static + SlotClock + Clone, E: EthSpec>(
                                     voting_password,
                                     body.enable,
                                     graffiti,
+                                    suggested_fee_recipient,
                                 ))
                                 .map_err(|e| {
                                     warp_utils::reject::custom_server_error(format!(

validator_client/src/http_api/tests.rs

@@ -267,6 +267,7 @@ impl ApiTester {
                 enable: !s.disabled.contains(&i),
                 description: format!("boi #{}", i),
                 graffiti: None,
+                suggested_fee_recipient: None,
                 deposit_gwei: E::default_spec().max_effective_balance,
             })
             .collect::<Vec<_>>();
@@ -397,6 +398,7 @@ impl ApiTester {
                     .into(),
                 keystore,
                 graffiti: None,
+                suggested_fee_recipient: None,
             };
 
             self.client
@@ -414,6 +416,7 @@ impl ApiTester {
                 .into(),
             keystore,
             graffiti: None,
+            suggested_fee_recipient: None,
         };
 
         let response = self
@@ -449,6 +452,7 @@ impl ApiTester {
                     enable: s.enabled,
                     description: format!("{}", i),
                     graffiti: None,
+                    suggested_fee_recipient: None,
                     voting_public_key: kp.pk,
                     url: format!("http://signer_{}.com/", i),
                     root_certificate_path: None,
@@ -574,6 +578,7 @@ fn routes_with_invalid_auth() {
                         enable: <_>::default(),
                         description: <_>::default(),
                         graffiti: <_>::default(),
+                        suggested_fee_recipient: <_>::default(),
                         deposit_gwei: <_>::default(),
                     }])
                     .await
@@ -602,6 +607,7 @@ fn routes_with_invalid_auth() {
                         enable: <_>::default(),
                         keystore,
                         graffiti: <_>::default(),
+                        suggested_fee_recipient: <_>::default(),
                     })
                     .await
             })

validator_client/src/http_api/tests/keystores.rs

@@ -37,6 +37,7 @@ fn web3signer_validator_with_pubkey(pubkey: PublicKey) -> Web3SignerValidatorReq
         enable: true,
         description: "".into(),
         graffiti: None,
+        suggested_fee_recipient: None,
         voting_public_key: pubkey,
         url: web3_signer_url(),
         root_certificate_path: None,