Merge #19644: rpc: document returned error fields as optional if applicable

f110b7c722eb150816a26cab161ac2b8c0f58609 rpc: document returned error fields as optional if applicable (Sebastian Falbesoner)

Pull request description:

  The following RPCs return error fields (named `"error"` or `"errors"`) that are optional, but don't show up as optional in the help text yet:
  * `analyzepsbt`
  * `estimatesmartfee`
  * `signrawtransactionwithkey`
  * `signrawtransactionwithwallet`

  The following RPC has the errors field already marked as optional, but doesn't match the usual format in the description (like `"if there are any"` in parantheses):
  * `estimaterawfee`

  This PR adds the missing optional flags and adapts the description strings. Inspired by a recent PR #19634 by justinmoon.

  The instances were found via `git grep "RPCResult.*\"error"`. Note that there is one RPC so far where the return error is not optional (i.e. in case of no error, the field is included in the result, but is just empty), namely `bumpfee`.

ACKs for top commit:
  adaminsky:
    ACK `f110b7c`
  laanwj:
    ACK f110b7c722eb150816a26cab161ac2b8c0f58609, new documentation looks consistent with actual behavior
  achow101:
    ACK f110b7c722eb150816a26cab161ac2b8c0f58609
  meshcollider:
    utACK f110b7c722eb150816a26cab161ac2b8c0f58609

Tree-SHA512: 30c00f78a575b60e32b4536496af986d53a25f33e6ebbf553adcdcf825ad21a44f90267f3d1ea53326dac83bcfa9983fdb3dad6d3126e20f97f3c08ce286e188

0 files changed, 0 insertions, 0 deletions