We test both the happy path (valid memo is returned when querying),
as well as the unhappy path (invalid memo rejects the open action).
To accomplish this, we update the OpenChannelParams struct inside
the harness to accept the Memo.
This commit enhances the custom fee policy channel open test by adding a
second channel and testing forwarding payments through the channel with
the custom forwarding policies.
This was able to reproduce the bug reported in #5796 which was fixed in
a previous commit of this PR.
