[backport#16326] [RPC] add new utxoupdatepsbt arguments to the CRPCCommand and CPRCConvertParam tables

Summary:
The new descriptors argument needs to be added to the Command and
ConvertParams tables to by usable as a named argument and by
bitcoin-cli.

Also update the test to use named arguments to test this.

Backport of Core PR16326

Test Plan:

ninja
test_runner.py rpc_psbt

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6660