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_test.go

@@ -0,0 +1,26 @@
+package structs
+
+import (
+	"testing"
+
+	eth "github.com/prysmaticlabs/prysm/v4/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/v4/testing/require"
+)
+
+func TestDepositSnapshotFromConsensus(t *testing.T) {
+	ds := &eth.DepositSnapshot{
+		Finalized:      [][]byte{{0xde, 0xad, 0xbe, 0xef}, {0xca, 0xfe, 0xba, 0xbe}},
+		DepositRoot:    []byte{0xab, 0xcd},
+		DepositCount:   12345,
+		ExecutionHash:  []byte{0x12, 0x34},
+		ExecutionDepth: 67890,
+	}
+
+	res := DepositSnapshotFromConsensus(ds)
+	require.NotNil(t, res)
+	require.DeepEqual(t, []string{"0xdeadbeef", "0xcafebabe"}, res.Finalized)
+	require.Equal(t, "0xabcd", res.DepositRoot)
+	require.Equal(t, "12345", res.DepositCount)
+	require.Equal(t, "0x1234", res.ExecutionBlockHash)
+	require.Equal(t, "67890", res.ExecutionBlockHeight)
+}