Implement conversions JSON->GRPC for requests type and GRPC->JSON for repsonses types

[RCasatta]

This could be useful for existing software with a JSON interface that wants to mimic the interface

Also, this enables tests to do roundtripping of the requests and response objects and check results are equal to initial value. Unfortunately this is not always the case at this stage and assert_eq!() on test_listpeers is commented out at the moment

Changelog-None

[RCasatta]

Removing draft since CI is passing, however, it's probably better to go after #5907 and (#5904 or #5902) to have some successful roundtrips in tests

[vincenzopalazzo]

Removing draft since CI is passing, however, it's probably better to go after #5907 and (#5904 or #5902) to have some successful roundtrips in tests

Yeah, I rerun the CI so if will pass (if not is postgress flaky problem) we can ping somebody to get it merge before the rc1

[RCasatta]

Rebased after #5907 and #5904 have been merged.
Now also test_getinfo roundtrips ok

[cdecker]

ACK 37bec26

[cdecker]

Rebased on top of master, let's see if it passes CI cleanly :-)

[cdecker]

And another rebase and update, to pick up num_channels which was added on master

[endothermicdev]

ACK 0447795