Merge bitcoin/bitcoin#26467: bumpfee: Allow the user to choose which output is change

e8c31f135c tests: Test for bumping single output transaction (Andrew Chow)
4f4d4407e3 test: Test bumpfee reduce_output (Andrew Chow)
7d83502d3d bumpfee: Allow original change position to be specified (Andrew Chow)

Pull request description:

  When bumping the transaction fee, we will try to find the change output of the transaction in order to have an output whose value we can modify so that we can meet the target feerate. However we do not always find the change output which can cause us to unnecessarily add an additional output to the transaction. We can avoid this issue by outsourcing the determination of change to the user if they so desire.

  This PR adds a `orig_change_pos` option to bumpfee which the user can use to specify the index of the change output.

  Fixes #11233
  Fixes #20795

ACKs for top commit:
  ismaelsadeeq:
    re ACK e8c31f135c
  pinheadmz:
    re-ACK e8c31f135c
  furszy:
    Code review ACK e8c31f13

Tree-SHA512: 3a230655934af17f7c1a5953fafb5ef0d687c21355cf284d5e98fece411f589cd69ea505f06d6bdcf82836b08d268c366ad2dd30ae3d71541c9cdf94d1f698ee

src/rpc/client.cpp

@@ -259,11 +259,13 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "bumpfee", 1, "fee_rate"},
     { "bumpfee", 1, "replaceable"},
     { "bumpfee", 1, "outputs"},
+    { "bumpfee", 1, "reduce_output"},
     { "psbtbumpfee", 1, "options" },
     { "psbtbumpfee", 1, "conf_target"},
     { "psbtbumpfee", 1, "fee_rate"},
     { "psbtbumpfee", 1, "replaceable"},
     { "psbtbumpfee", 1, "outputs"},
+    { "psbtbumpfee", 1, "reduce_output"},
     { "logging", 0, "include" },
     { "logging", 1, "exclude" },
     { "disconnectnode", 1, "nodeid" },