chore(core): Log kas URI on key index requests (#2710)

### Proposed Changes

* This is helpful for figuring out if the index is misconfigured

### Checklist

- [ ] I have added or updated unit tests
- [ ] I have added or updated integration tests (if appropriate)
- [ ] I have added or updated documentation

### Testing Instructions

Author: dmihalcik-virtru

service/kas/key_indexer.go

@@ -81,6 +81,10 @@ func convertAlgToEnum(alg string) (policy.Algorithm, error) {
 	}
 }
 
+func (p *KeyIndexer) String() string {
+	return fmt.Sprintf("PlatformKeyIndexer[%s]", p.kasURI)
+}
+
 func (p *KeyIndexer) FindKeyByAlgorithm(ctx context.Context, algorithm string, includeLegacy bool) (trust.KeyDetails, error) {
 	alg, err := convertAlgToEnum(algorithm)
 	if err != nil {

service/trust/delegating_key_service.go

@@ -90,7 +90,7 @@ func (d *DelegatingKeyService) Name() string {
 func (d *DelegatingKeyService) Decrypt(ctx context.Context, keyID KeyIdentifier, ciphertext []byte, ephemeralPublicKey []byte) (ProtectedKey, error) {
 	keyDetails, err := d.index.FindKeyByID(ctx, keyID)
 	if err != nil {
-		return nil, fmt.Errorf("unable to find key by ID '%s': %w", keyID, err)
+		return nil, fmt.Errorf("unable to find key by ID '%s' within index %s: %w", keyID, d.index, err)
 	}
 
 	manager, err := d.getKeyManager(keyDetails.System())
@@ -104,7 +104,7 @@ func (d *DelegatingKeyService) Decrypt(ctx context.Context, keyID KeyIdentifier,
 func (d *DelegatingKeyService) DeriveKey(ctx context.Context, keyID KeyIdentifier, ephemeralPublicKeyBytes []byte, curve elliptic.Curve) (ProtectedKey, error) {
 	keyDetails, err := d.index.FindKeyByID(ctx, keyID)
 	if err != nil {
-		return nil, fmt.Errorf("unable to find key by ID '%s': %w", keyID, err)
+		return nil, fmt.Errorf("unable to find key by ID '%s' in index %s: %w", keyID, d.index, err)
 	}
 
 	manager, err := d.getKeyManager(keyDetails.System())