test: Add p2p test for forcerelay permission

Summary:
This is a backport of core#17984

Backport note:

• Most of the PR is not relevant for us (segwit stuff or codestyle), so this includes only the commit that adds a useful new test for forcerelay permission.
• The code to build the transaction is different because Core uses some kind of dark magic to make a transaction that does not require a signature. I used a normal address and signed it, instead.

Test Plan: ninja check-functional

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9906