Add support for updating validator graffiti (#4417)

## Issue Addressed

#4386 

## Proposed Changes

The original proposal described in the issue adds a new endpoint to support updating validator graffiti, but I realized we already have an endpoint that we use for updating various validator fields in memory and in the validator definitions file, so I think that would be the best place to add this to.

### API endpoint

`PATCH lighthouse/validators/{validator_pubkey}` 

This endpoint updates the graffiti in both the [ validator definition file](https://lighthouse-book.sigmaprime.io/graffiti.html#2-setting-the-graffiti-in-the-validator_definitionsyml) and the in memory `InitializedValidators`. In the next block proposal, the new graffiti will be used.

Note that the [`--graffiti-file`](https://lighthouse-book.sigmaprime.io/graffiti.html#1-using-the---graffiti-file-flag-on-the-validator-client) flag has a priority over the validator definitions file, so if the caller attempts to update the graffiti while the `--graffiti-file` flag is present, the endpoint will return an error (Bad request 400).

## Tasks

- [x] Add graffiti update support to `PATCH lighthouse/validators/{validator_pubkey}` 
- [x] Return error if user tries to update graffiti while the `--graffiti-flag` is set
- [x] Update Lighthouse book

validator_client/src/http_api/tests.rs

@@ -28,12 +28,14 @@ use slot_clock::{SlotClock, TestingSlotClock};
 use std::future::Future;
 use std::marker::PhantomData;
 use std::net::{IpAddr, Ipv4Addr};
+use std::str::FromStr;
 use std::sync::Arc;
 use std::time::Duration;
 use task_executor::TaskExecutor;
 use tempfile::{tempdir, TempDir};
 use tokio::runtime::Runtime;
 use tokio::sync::oneshot;
+use types::graffiti::GraffitiString;
 
 const PASSWORD_BYTES: &[u8] = &[42, 50, 37];
 pub const TEST_DEFAULT_FEE_RECIPIENT: Address = Address::repeat_byte(42);
@@ -533,7 +535,7 @@ impl ApiTester {
         let validator = &self.client.get_lighthouse_validators().await.unwrap().data[index];
 
         self.client
-            .patch_lighthouse_validators(&validator.voting_pubkey, Some(enabled), None, None)
+            .patch_lighthouse_validators(&validator.voting_pubkey, Some(enabled), None, None, None)
             .await
             .unwrap();
 
@@ -575,7 +577,13 @@ impl ApiTester {
         let validator = &self.client.get_lighthouse_validators().await.unwrap().data[index];
 
         self.client
-            .patch_lighthouse_validators(&validator.voting_pubkey, None, Some(gas_limit), None)
+            .patch_lighthouse_validators(
+                &validator.voting_pubkey,
+                None,
+                Some(gas_limit),
+                None,
+                None,
+            )
             .await
             .unwrap();
 
@@ -602,6 +610,7 @@ impl ApiTester {
                 None,
                 None,
                 Some(builder_proposals),
+                None,
             )
             .await
             .unwrap();
@@ -620,6 +629,34 @@ impl ApiTester {
 
         self
     }
+
+    pub async fn set_graffiti(self, index: usize, graffiti: &str) -> Self {
+        let validator = &self.client.get_lighthouse_validators().await.unwrap().data[index];
+        let graffiti_str = GraffitiString::from_str(graffiti).unwrap();
+        self.client
+            .patch_lighthouse_validators(
+                &validator.voting_pubkey,
+                None,
+                None,
+                None,
+                Some(graffiti_str),
+            )
+            .await
+            .unwrap();
+
+        self
+    }
+
+    pub async fn assert_graffiti(self, index: usize, graffiti: &str) -> Self {
+        let validator = &self.client.get_lighthouse_validators().await.unwrap().data[index];
+        let graffiti_str = GraffitiString::from_str(graffiti).unwrap();
+        assert_eq!(
+            self.validator_store.graffiti(&validator.voting_pubkey),
+            Some(graffiti_str.into())
+        );
+
+        self
+    }
 }
 
 struct HdValidatorScenario {
@@ -723,7 +760,13 @@ fn routes_with_invalid_auth() {
             .await
             .test_with_invalid_auth(|client| async move {
                 client
-                    .patch_lighthouse_validators(&PublicKeyBytes::empty(), Some(false), None, None)
+                    .patch_lighthouse_validators(
+                        &PublicKeyBytes::empty(),
+                        Some(false),
+                        None,
+                        None,
+                        None,
+                    )
                     .await
             })
             .await
@@ -931,6 +974,41 @@ fn validator_builder_proposals() {
     });
 }
 
+#[test]
+fn validator_graffiti() {
+    let runtime = build_runtime();
+    let weak_runtime = Arc::downgrade(&runtime);
+    runtime.block_on(async {
+        ApiTester::new(weak_runtime)
+            .await
+            .create_hd_validators(HdValidatorScenario {
+                count: 2,
+                specify_mnemonic: false,
+                key_derivation_path_offset: 0,
+                disabled: vec![],
+            })
+            .await
+            .assert_enabled_validators_count(2)
+            .assert_validators_count(2)
+            .set_graffiti(0, "Mr F was here")
+            .await
+            .assert_graffiti(0, "Mr F was here")
+            .await
+            // Test setting graffiti while the validator is disabled
+            .set_validator_enabled(0, false)
+            .await
+            .assert_enabled_validators_count(1)
+            .assert_validators_count(2)
+            .set_graffiti(0, "Mr F was here again")
+            .await
+            .set_validator_enabled(0, true)
+            .await
+            .assert_enabled_validators_count(2)
+            .assert_graffiti(0, "Mr F was here again")
+            .await
+    });
+}
+
 #[test]
 fn keystore_validator_creation() {
     let runtime = build_runtime();