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/node/interfaces.cpp

@@ -363,7 +363,12 @@ public:
     }
     TransactionError broadcastTransaction(CTransactionRef tx, CAmount max_tx_fee, std::string& err_string) override
     {
-        return BroadcastTransaction(*m_context, std::move(tx), err_string, max_tx_fee, /*relay=*/ true, /*wait_callback=*/ false);
+        return BroadcastTransaction(*m_context,
+                                    std::move(tx),
+                                    err_string,
+                                    max_tx_fee,
+                                    TxBroadcast::MEMPOOL_AND_BROADCAST_TO_ALL,
+                                    /*wait_callback=*/false);
     }
     WalletLoader& walletLoader() override
     {
@@ -672,10 +677,10 @@ public:
     }
     bool broadcastTransaction(const CTransactionRef& tx,
         const CAmount& max_tx_fee,
-        bool relay,
+        TxBroadcast broadcast_method,
         std::string& err_string) override
     {
-        const TransactionError err = BroadcastTransaction(m_node, tx, err_string, max_tx_fee, relay, /*wait_callback=*/false);
+        const TransactionError err = BroadcastTransaction(m_node, tx, err_string, max_tx_fee, broadcast_method, /*wait_callback=*/false);
         // Chain clients only care about failures to accept the tx to the mempool. Disregard non-mempool related failures.
         // Note: this will need to be updated if BroadcastTransactions() is updated to return other non-mempool failures
         // that Chain clients do not need to know about.