Accountsdb replication installment 2 (#19325)

This is the 2nd installment for the AccountsDb replication.

Summary of Changes

The basic google protocol buffer protocol for replicating updated slots and accounts. tonic/tokio is used for transporting the messages.

The basic framework of the client and server for replicating slots and accounts -- the persisting of accounts in the replica-side will be done at the next PR -- right now -- the accounts are streamed to the replica-node and dumped. Replication for information about Bank is also not done in this PR -- to be addressed in the next PR to limit the change size.

Functionality used by both the client and server side are encapsulated in the replica-lib crate.

There is no impact to the existing validator by default.

Tests:

Observe the confirmed slots replicated to the replica-node.
Observe the accounts for the confirmed slot are received at the replica-node side.

replica-lib/proto/accountsdb_repl.proto

@@ -0,0 +1,44 @@
+
+// version of prorocol buffer used
+syntax = "proto3";
+
+package accountsdb_repl;
+
+message ReplicaSlotConfirmationRequest {
+    uint64 last_replicated_slot = 1;
+}
+
+message ReplicaSlotConfirmationResponse {
+    repeated uint64 updated_slots = 1;
+}
+
+message ReplicaAccountsRequest {
+    uint64 slot = 1;
+}
+
+message ReplicaAccountMeta {
+    bytes Pubkey = 1;
+    uint64 lamports = 2;
+    bytes owner = 3;
+    bool executable = 4;
+    uint64 rent_epoch = 5;
+}
+
+message ReplicaAccountData {
+    bytes data = 1;
+}
+
+message ReplicaAccountInfo {
+    ReplicaAccountMeta account_meta = 1;
+    bytes hash = 2;
+    ReplicaAccountData data = 3;
+}
+
+message ReplicaAccountsResponse {
+    repeated ReplicaAccountInfo accounts = 1;
+}
+
+service AccountsDbRepl {
+    rpc get_confirmed_slots(ReplicaSlotConfirmationRequest) returns (ReplicaSlotConfirmationResponse);
+    rpc get_slot_accounts(ReplicaAccountsRequest) returns (ReplicaAccountsResponse);
+}