Validator announce signers (#2617)

### Description

This handles a bug where we did not default the chain signer to the
validator signature for EVM chains and also handles the case where we
might try to announce without setting a chain signer for other chains.

### Drive-by changes

Not really a change but I looked into #2457 and I noticed the validators
already check that signers are set for all destination chains so I think
the error was just for validators which this PR fixes.

### Related issues

- Fixes #2458
- Fixes  #2457

### Backward compatibility

Yes

### Testing

Unit Tests

rust/agents/validator/src/settings.rs

@@ -10,7 +10,7 @@ use hyperlane_base::{
     SignerConf,
 };
 use hyperlane_core::config::*;
-use hyperlane_core::HyperlaneDomain;
+use hyperlane_core::{HyperlaneDomain, HyperlaneDomainProtocol};
 
 decl_settings!(Validator,
     Parsed {
@@ -54,7 +54,7 @@ impl FromRawConf<'_, RawValidatorSettings> for ValidatorSettings {
 
         let validator = raw
             .validator
-            .parse_config(&cwp.join("validator"))
+            .parse_config::<SignerConf>(&cwp.join("validator"))
             .take_config_err(&mut err);
 
         let checkpoint_syncer = raw
@@ -112,11 +112,26 @@ impl FromRawConf<'_, RawValidatorSettings> for ValidatorSettings {
         });
 
         err.into_result()?;
+
+        let mut base = base.unwrap();
+        let origin_chain = origin_chain.unwrap();
+        let validator = validator.unwrap();
+
+        if origin_chain.domain_protocol() == HyperlaneDomainProtocol::Ethereum {
+            // if an EVM chain we can assume the chain signer is the validator signer when not
+            // specified
+            base.chains
+                .get_mut(origin_chain.name())
+                .unwrap()
+                .signer
+                .get_or_insert_with(|| validator.clone());
+        }
+
         Ok(Self {
-            base: base.unwrap(),
+            base,
             db,
-            origin_chain: origin_chain.unwrap(),
+            origin_chain,
-            validator: validator.unwrap(),
+            validator,
             checkpoint_syncer: checkpoint_syncer.unwrap(),
             reorg_period: reorg_period.unwrap(),
             interval,

rust/agents/validator/src/validator.rs

@@ -226,6 +226,14 @@ impl Validator {
     }
 
     async fn announce(&self) -> Result<()> {
+        if self.core.settings.chains[self.origin_chain.name()]
+            .signer
+            .is_none()
+        {
+            warn!(origin_chain=%self.origin_chain, "Cannot announce validator without a signer; make sure a signer is set for the origin chain");
+            return Ok(());
+        }
+
         // Sign and post the validator announcement
         let announcement = Announcement {
             validator: self.signer.eth_address(),