Candidate validation subsytem

[kishansagathiya]

Issue summary

This subsystem is responsible for handling candidate validation requests. It is a simple request/response server.

We have some work done for this. Look at dot/parachain/candidate_validation.go and dot/parachain/candidate_validation_test.go. But there are a decent amount of things remaining.

Sub Issues

• feat(dot/parachain): create a skeleton for candidate validation subsystem and register it with overseer #3586
• Implement candidate validation processing for ValidateFromChainState message  #3919
• Implement candidate validation processing for ValidateFromExhaustive message #3920
• Implement candidate validation for 'PreCheck' message #3921
• Make sure that all of the errors meant for invalidity can happen in candidate validation #3426
• Add candidate validation messages #3496
• feat(dot/parachain): validate a candidate with provided exhaustive parameters for validation #3547
• ignore overseer signals
• Investigate PVF Host for candidate validation subsystem #3934

Other information and links

• https://paritytech.github.io/polkadot-sdk/book/node/utility/candidate-validation.html

[timwu20]

@edwardmack please create the remaining issues regarding this subsystem.

[edwardmack]

@edwardmack please create the remaining issues regarding this subsystem.

I've created issues #3919, #3920 and #3921 to address different message types ValidateFromChain, ValidateFromExhaustive and PreCheck

I've also created an issue to address implementation of the PVF host (#3934), there is a lot to the PVF host, so that issue may be broken into subissues when we have a better understanding of the full scope.