Improve git commit hash lookup (#5225)

- Also get the branch name.
- Use rev-parse instead of describe to get a clean hash.
- Return the git hash and branch name in server_info for admin
  connections.
- Include git hash and branch name on separate lines in --version.

include/xrpl/protocol/jss.h

@@ -199,6 +199,7 @@ JSS(blobs_v2);         // out: ValidatorList
 JSS(books);            // in: Subscribe, Unsubscribe
 JSS(both);             // in: Subscribe, Unsubscribe
 JSS(both_sides);       // in: Subscribe, Unsubscribe
+JSS(branch);           // out: server_info
 JSS(broadcast);        // out: SubmitTransaction
 JSS(bridge_account);   // in: LedgerEntry
 JSS(build_path);       // in: TransactionSign
@@ -336,6 +337,7 @@ JSS(frozen_balances);       // out: GatewayBalances
 JSS(full);                  // in: LedgerClearer, handlers/Ledger
 JSS(full_reply);            // out: PathFind
 JSS(fullbelow_size);        // out: GetCounts
+JSS(git);                   // out: server_info
 JSS(good);                  // out: RPCVersion
 JSS(hash);                  // out: NetworkOPs, InboundLedger,
 JSS(hash_mismatches);       // out: catalogue