Detect storage migration requirements in CI

[ggwpez]

Sometimes it is not obvious if a type is stored in storage and would need a storage migration.
We can automate this detection with Subwasm by applying it to the Kitchensink runtime, which has all (?) pallets deployed.
Subwasm can detect metadata changes to storage definitions. Such a change always necessitate a migration.
We can then add a label or somehow silence the check one a migration was added.

I opened this issue here so we can play around with it a bit in Substrate, and once its proven to work roll it out to Polkadot and Cumulus as well.

[ggwpez]

One recent example where we forgot a migration was in: paritytech/substrate#13128.
It migrated the BondedPools map, but not the RewardPools map which had to be hot-fixed in paritytech/substrate#13715.
So the check can be tested with that MR to detect both maps as "must migrate".

[kianenigma]

Subwasm can detect metadata changes to storage definitions. Such a change always necessitate a migration.

Stumbled upon https://github.com/hack-ink/subalfred-check-runtime-action which can also do the same, and it is already packaged as a GH action.