Add zombienet tests for malicious collators

[alindima]

AFAICT we don't have zombienet tests for malicious collators and checking their potential impact on the network.

Some scenarios off the top of my head:

• collators trying to DOS backers by overloading them with advertisements/collations (check that the reputation changes provide a reasonable mitigation)
• collators providing invalid collations. the other honest collators should still be able to get blocks in.
• collators deliberately creating parachain forks. throughput should decrease but the parachain should not stall.

[sandreim]

This is more than just tests, we need a malus-test-collator.

[bkchr]

This is more than just tests, we need a malus-test-collator.

For nothing of what is said above, you need a "malus collator". You basically just need to send junk.

[alindima]

another test scenario: collator spamming validators with chunk requests for pov recovery