qa: Run feature_block tests on p2p and rpc interface #14789

submitblock is a relatively tight RPC wrapper around ProcessNewBlock and thus does the same things as submitting a block message on the p2p network interface.

So we can spin up two nodes in feature_block and have each of them test one interface. Most of the code and reject messages in feature_block.py can be reused for that.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #14457 (test: add invalid tx templates for use in functional tests by jamesob)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.