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>

lighthouse/tests/account_manager.rs

@@ -493,6 +493,7 @@ fn validator_import_launchpad() {
         enabled: false,
         description: "".into(),
         graffiti: None,
+        suggested_fee_recipient: None,
         voting_public_key: keystore.public_key().unwrap(),
         signing_definition: SigningDefinition::LocalKeystore {
             voting_keystore_path,
@@ -612,6 +613,7 @@ fn validator_import_launchpad_no_password_then_add_password() {
         enabled: true,
         description: "".into(),
         graffiti: None,
+        suggested_fee_recipient: None,
         voting_public_key: keystore.public_key().unwrap(),
         signing_definition: SigningDefinition::LocalKeystore {
             voting_keystore_path,
@@ -635,6 +637,7 @@ fn validator_import_launchpad_no_password_then_add_password() {
         enabled: true,
         description: "".into(),
         graffiti: None,
+        suggested_fee_recipient: None,
         voting_public_key: keystore.public_key().unwrap(),
         signing_definition: SigningDefinition::LocalKeystore {
             voting_keystore_path: dst_keystore_dir.join(KEYSTORE_NAME),
@@ -734,6 +737,7 @@ fn validator_import_launchpad_password_file() {
         description: "".into(),
         voting_public_key: keystore.public_key().unwrap(),
         graffiti: None,
+        suggested_fee_recipient: None,
         signing_definition: SigningDefinition::LocalKeystore {
             voting_keystore_path,
             voting_keystore_password_path: None,

lighthouse/tests/beacon_node.rs

@@ -212,7 +212,7 @@ fn merge_fee_recipient_flag() {
     CommandLineTest::new()
         .flag("merge", None)
         .flag(
-            "fee-recipient",
+            "suggested-fee-recipient",
             Some("0x00000000219ab540356cbb839cbe05303d7705fa"),
         )
         .run_with_zero_port()

lighthouse/tests/validator_client.rs

@@ -7,8 +7,10 @@ use std::io::Write;
 use std::net::Ipv4Addr;
 use std::path::PathBuf;
 use std::process::Command;
+use std::str::FromStr;
 use std::string::ToString;
 use tempfile::TempDir;
+use types::Address;
 
 /// Returns the `lighthouse validator_client` command.
 fn base_cmd() -> Command {
@@ -218,6 +220,83 @@ fn graffiti_file_with_pk_flag() {
         });
 }
 
+// Tests for suggested-fee-recipient flags.
+#[test]
+fn fee_recipient_flag() {
+    CommandLineTest::new()
+        .flag(
+            "suggested-fee-recipient",
+            Some("0x00000000219ab540356cbb839cbe05303d7705fa"),
+        )
+        .run()
+        .with_config(|config| {
+            assert_eq!(
+                config.fee_recipient,
+                Some(Address::from_str("0x00000000219ab540356cbb839cbe05303d7705fa").unwrap())
+            )
+        });
+}
+#[test]
+fn fee_recipient_file_flag() {
+    let dir = TempDir::new().expect("Unable to create temporary directory");
+    let mut file =
+        File::create(dir.path().join("fee_recipient.txt")).expect("Unable to create file");
+    let new_key = Keypair::random();
+    let pubkeybytes = PublicKeyBytes::from(new_key.pk);
+    let contents = "default:0x00000000219ab540356cbb839cbe05303d7705fa";
+    file.write_all(contents.as_bytes())
+        .expect("Unable to write to file");
+    CommandLineTest::new()
+        .flag(
+            "suggested-fee-recipient-file",
+            dir.path().join("fee_recipient.txt").as_os_str().to_str(),
+        )
+        .run()
+        .with_config(|config| {
+            // Public key not present so load default.
+            assert_eq!(
+                config
+                    .fee_recipient_file
+                    .clone()
+                    .unwrap()
+                    .load_fee_recipient(&pubkeybytes)
+                    .unwrap(),
+                Some(Address::from_str("0x00000000219ab540356cbb839cbe05303d7705fa").unwrap())
+            )
+        });
+}
+#[test]
+fn fee_recipient_file_with_pk_flag() {
+    let dir = TempDir::new().expect("Unable to create temporary directory");
+    let mut file =
+        File::create(dir.path().join("fee_recipient.txt")).expect("Unable to create file");
+    let new_key = Keypair::random();
+    let pubkeybytes = PublicKeyBytes::from(new_key.pk);
+    let contents = format!(
+        "{}:0x00000000219ab540356cbb839cbe05303d7705fa",
+        pubkeybytes.to_string()
+    );
+    file.write_all(contents.as_bytes())
+        .expect("Unable to write to file");
+    CommandLineTest::new()
+        .flag(
+            "suggested-fee-recipient-file",
+            dir.path().join("fee_recipient.txt").as_os_str().to_str(),
+        )
+        .run()
+        .with_config(|config| {
+            assert_eq!(
+                config
+                    .fee_recipient_file
+                    .clone()
+                    .unwrap()
+                    .load_fee_recipient(&pubkeybytes)
+                    .unwrap(),
+                Some(Address::from_str("0x00000000219ab540356cbb839cbe05303d7705fa").unwrap())
+            )
+        });
+}
+
 // Tests for HTTP flags.
 #[test]
 fn http_flag() {