docs: Document safe use of Twox64Concat

[weichweich]

fixes https://github.com/KILTprotocol/ticket/issues/2529

Metadata Diff to Develop Branch

Peregrine Diff

!!! THE SUBWASM REDUCED DIFFER IS EXPERIMENTAL, DOUBLE CHECK THE RESULTS !!!
No change detected
SUMMARY:
- Compatible.......................: true
- Require transaction_version bump.: false

!!! THE SUBWASM REDUCED DIFFER IS EXPERIMENTAL, DOUBLE CHECK THE RESULTS !!!

Spiritnet Diff

!!! THE SUBWASM REDUCED DIFFER IS EXPERIMENTAL, DOUBLE CHECK THE RESULTS !!!
No change detected
SUMMARY:
- Compatible.......................: true
- Require transaction_version bump.: false

!!! THE SUBWASM REDUCED DIFFER IS EXPERIMENTAL, DOUBLE CHECK THE RESULTS !!!

Checklist:

• [ ] I have verified that the code works
  • [ ] No panics! (checked arithmetic ops, no indexing array[3] use get(3), ...)
• [ ] I have verified that the code is easy to understand
  • [ ] If not, I have left a well-balanced amount of inline comments
• [ ] I have left the code in a better state
• [ ] I have documented the changes (where applicable)
  • Either PR or Ticket to update the Docs
  • Link the PR/Ticket here

[weichweich]

• [ ] check Metadata and SDK compatibility before merging

[ntn-x2]

This will break cross-chain DIP proofs since the storage keys (and the related proofs) have changed, hence we might want to change at least the DIP stuff to make it resistant.

[ntn-x2]

DIP stuff was fixed in https://github.com/KILTprotocol/kilt-node/pull/613.

[ntn-x2]

I'm putting this on hold until we get to a polkadot-sdk version that supports multi-block-migrations, after which we can revise this PR and perform the necessary migrations.