Merge bitcoin/bitcoin#25610: wallet, rpc: Opt in to RBF by default

ab3c06db1a doc: Release notes for default RBF (Andrew Chow)
61d9149e78 rpc: Default rbf enabled (Andrew Chow)
e3c33637ba wallet: Enable -walletrbf by default (Andrew Chow)

Pull request description:

  The GUI currently opts in to RBF by default, but RPCs do not, and `-walletrbf` is default disabled. This PR makes the default in those two places to also opt in.

  The last time this was proposed (#9527), the primary objections were the novelty at the time, the inability to bump transactions, and the gui not having the option to disable rbf. In the 5 years since, RBF usage has steadily grown, with ~27% of txs opting in. The GUI has the option to enable/disable RBF, and is also defaulted to having it enabled. And we have the ability to bump RBF'd transactions in both the RPC and the GUI. So I think it makes sense to finally change the default to always opt in to RBF.

ACKs for top commit:
  darosior:
    reACK ab3c06db1a
  aureleoules:
    ACK ab3c06db1a.
  glozow:
    utACK ab3c06db1a

Tree-SHA512: 81b012c5033e270f86a87a6a196ccc549eb54b158eebf88e917cc6621d40d7bdcd1566b602688907dd5d364b95a557b29f97dce869cea512e339588262c027b6

doc/release-notes-25610.md

@@ -0,0 +1,12 @@
+Wallet
+------
+
+- The `-walletrbf` startup option will now default to `true`. The
+  wallet will now default to opt-in RBF on transactions that it creates.
+
+Updated RPCs
+------------
+
+- The `replaceable` option for the `createrawtransaction` and
+  `createpsbt` RPCs will now default to `true`. Transactions created
+  with these RPCs will default to having opt-in RBF enabled.