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/build.rs

@@ -0,0 +1,5 @@
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // compiling protos using path on build time
+    tonic_build::configure().compile(&["proto/accountsdb_repl.proto"], &["proto"])?;
+    Ok(())
+}