Merge bitcoin/bitcoin#33567: node: change a tx-relay on/off flag to enum

07a926474b node: change a tx-relay on/off flag to enum (Vasil Dimov)

Pull request description:

  Previously the `bool relay` argument to `BroadcastTransaction()` designated:

  ```
  relay=true: add to the mempool and broadcast to all peers
  relay=false: add to the mempool
  ```

  Change this to an `enum`, so it is more readable and easier to extend with a 3rd option. Consider these example call sites:

  ```cpp
  Paint(true);
  // Or
  Paint(/*is_red=*/true);
  ```

  vs

  ```cpp
  Paint(RED);
  ```

  The idea for putting `TxBroadcastMethod` into `node/types.h` by Ryan.

  ---

  This is part of [#29415 Broadcast own transactions only via short-lived Tor or I2P connections](https://github.com/bitcoin/bitcoin/pull/29415). Putting it in its own PR to reduce the size of #29415 and because it does not logically depend on the other commits from there.

ACKs for top commit:
  optout21:
    ACK 07a926474b
  kevkevinpal:
    ACK [07a9264](07a926474b)
  laanwj:
    Concept and code review ACK 07a926474b. Agree with the general reasoning and the change in #29415 is a valid motivation to change this interface.
  glozow:
    utACK 07a926474b

Tree-SHA512: ec8f6fa56a6d2422a0fbd5941ff2792685e8d8e7b9dd50bba9f3e21ed9b4a4a26c89b0d7e4895d48f30b7a635f2eddd894af26b5266410952cbdaf5c40b42966

src/rpc/mempool.cpp

@@ -98,7 +98,12 @@ static RPCHelpMan sendrawtransaction()
             std::string err_string;
             AssertLockNotHeld(cs_main);
             NodeContext& node = EnsureAnyNodeContext(request.context);
-            const TransactionError err = BroadcastTransaction(node, tx, err_string, max_raw_tx_fee, /*relay=*/true, /*wait_callback=*/true);
+            const TransactionError err = BroadcastTransaction(node,
+                                                              tx,
+                                                              err_string,
+                                                              max_raw_tx_fee,
+                                                              node::TxBroadcast::MEMPOOL_AND_BROADCAST_TO_ALL,
+                                                              /*wait_callback=*/true);
             if (TransactionError::OK != err) {
                 throw JSONRPCTransactionError(err, err_string);
             }
@@ -1068,7 +1073,12 @@ static RPCHelpMan submitpackage()
 
                 // We do not expect an error here; we are only broadcasting things already/still in mempool
                 std::string err_string;
-                const auto err = BroadcastTransaction(node, tx, err_string, /*max_tx_fee=*/0, /*relay=*/true, /*wait_callback=*/true);
+                const auto err = BroadcastTransaction(node,
+                                                      tx,
+                                                      err_string,
+                                                      /*max_tx_fee=*/0,
+                                                      node::TxBroadcast::MEMPOOL_AND_BROADCAST_TO_ALL,
+                                                      /*wait_callback=*/true);
                 if (err != TransactionError::OK) {
                     throw JSONRPCTransactionError(err,
                         strprintf("transaction broadcast failed: %s (%d transactions were broadcast successfully)",