Zombienet: test disputes with malus garbage candidates

[sandreim]

trafficstars

Replaces dangling PR https://github.com/paritytech/polkadot/pull/5020

[sandreim]

Looks good, but I wonder how flaky this test will be.

Maybe we can reduce the number of parachains to 1 or 2, we don't need 7 for this test. It's also worth mentioning that we rely on suggest-garbage-candidate to back garbage candidate of others and we need at least 2 of them for backing to work.

Yeah, scaling it down makes it less flaky.

[sandreim]

bot merge