Tests for PSBT

Summary:
Added functional tests for PSBT that test the RPCs. Also added all
of the BIP 174 test vectors (except for the updater tests) in the
functional tests.

Added a Unit test for the BIP 174 updater test vector.

This is a partial backport of Core PR13557 : https://github.com/bitcoin/bitcoin/pull/13557/commits/020628e3a4e88e36647eaf92bac4b3552796ac6a

Depends on D4352

Test Plan:

make check
./test/functionnal/test_runner.py rpc_psbt

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4353