Add /eth/v1/beacon/deposit_snapshot endpoint (#13514)

* Add endpoint

* Uncomment in InitializeRoutes

* Add test

* Add 404

* Add more checks

* Test improvements

* Ssz

* Add ssz tags

* Add DepositSnapshot to bazel

* Fix tests

* Fix max size

* Resolve conflicts

* Revert untouched code

* Fix test + review

* Lint

* Oops

* Preston + Radek' review

* Only return 3 finalized roots

* Change to deposit contract depth

* Radek' review

* Gaz

---------

Co-authored-by: james-prysm <90280386+james-prysm@users.noreply.github.com>

api/server/structs/conversions.go

@@ -1074,3 +1074,17 @@ func sszBytesToUint256String(b []byte) (string, error) {
 	}
 	return bi.String(), nil
 }
+
+func DepositSnapshotFromConsensus(ds *eth.DepositSnapshot) *DepositSnapshot {
+	finalized := make([]string, 0, len(ds.Finalized))
+	for _, f := range ds.Finalized {
+		finalized = append(finalized, hexutil.Encode(f))
+	}
+	return &DepositSnapshot{
+		Finalized:            finalized,
+		DepositRoot:          hexutil.Encode(ds.DepositRoot),
+		DepositCount:         fmt.Sprintf("%d", ds.DepositCount),
+		ExecutionBlockHash:   hexutil.Encode(ds.ExecutionHash),
+		ExecutionBlockHeight: fmt.Sprintf("%d", ds.ExecutionDepth),
+	}
+}