Use relay chain block number in the broker pallet instead of block number

[davidk-pt]

Based on https://github.com/paritytech/polkadot-sdk/pull/3331

Implements migrations with customizable block number to relay height number translation function.

Adds block to relay height migration code for rococo and westend.

[xlc]

this will break all the UI and indexers and I am not sure if there exists a good solution...

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs. Job name: test-linux-stable 3/3 Logs: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7340522

[kianenigma]

this will break all the UI and indexers and I am not sure if there exists a good solution...

Yeah, only solution that comes to mind is something like https://github.com/polkadot-api/polkadot-api/issues/689

[xlc]

a backward compatible approach will be use relaychain block number / 2 + offset so we don’t need complicated migration and existing dapps will still be functional without changes

[joepetrowski]

a backward compatible approach will be use relaychain block number / 2 + offset so we don’t need complicated migration and existing dapps will still be functional without changes

Why would you use the RC block number? The offset should account for the difference in block height, but the coefficient (here, 1/2) should be w/r/t the block time.

[xlc]

the idea is simulate 12s block time regardless local block time so the meaning of the block numbers in storage stays the same and keep UI compatible

[joepetrowski]

I still don't understand from that description. So you are saying that if a parachain goes 24 second between two blocks, that those would be n and n+2?

[xlc]

Yes. I have bit more explanation here and maybe we should move the discussion over there as well https://github.com/paritytech/polkadot-sdk/issues/3268#issuecomment-2357045461