Merge bitcoin/bitcoin#31953: rpc: Allow fullrbf fee bump in (psbt)bumpfee

fa86190e6e rpc: Allow fullrbf fee bump (MarcoFalke)

Pull request description:

  The RPCs (psbt)bumpfee, and the GUI, reject fee bumps when BIP 125 signalling is absent in the transaction even when the mempool and other RPCs allow them. Fix the confusion by allowing the fee bump.

  This is done after fullrbf is always on (https://github.com/bitcoin/bitcoin/pull/30592)

ACKs for top commit:
  1440000bytes:
    reACK https://github.com/bitcoin/bitcoin/commit/fa86190e6ed2aeda7bcceaf96f52403816bcd751
  achow101:
    ACK fa86190e6e
  w0xlt:
    ACK https://github.com/bitcoin/bitcoin/pull/31953/commits/fa86190e6ed2aeda7bcceaf96f52403816bcd751
  rkrux:
    reACK fa86190e6e
  glozow:
    ACK fa86190e6e

Tree-SHA512: b2ffe8dcadbe71e9be767a16cf8aa0bf383c2de7aa1aee9438d125f444e24f3f7e4f02ddb28981bd3b8b645b6a24a407b4ad6bb0b21946ae637e78f6386e05bf

doc/release-notes-31953.md

@@ -0,0 +1,9 @@
+# RPC
+
+- The RPCs psbtbumpfee and bumpfee allow a replacement under fullrbf and no
+  longer require BIP-125 signalling. (#31953)
+
+# GUI
+
+- A transaction's fee bump is allowed under fullrbf and no longer requires
+  BIP-125 signalling. (#31953)