Instant seal consensus for better development experience

[h4x3rotab]

Nowadays the local dev testnet is configured to produce one block per 3 seconds. When doing local e2e test, it may slow down the test a lot since a lot of integration tests must be done sequentially. Substrate offers ManualSeal, an alternative consensus engine that allows to produce block instantly for testing. If we can adopt that, we can run test much faster.

However it turns out only a replacement of the consensu engine is not enough. We should do at least the followings:

1. Replace the Grandpa consensus by ManualSeal in phala-blockchain (phala-blockchain is for dev while khala-parachain is for production)
2. Allow to bypass grandpa block justification validation in pruntime for dev testnet
3. Allow to bypass block justification transmission logic in pherry for dev testnet

TODO

• A clear bounty definition
• Resources
• Post to Gitcoin.co