Allow whitelisting some keys for idempotency check

Recently we have had the try-runtime tool fail in tanssi because of a state mismatch when running the idempotent check. The cause was 2 keys in pallet system: events and eventsCount, which changed because one of our migrations emitted an event to signal the start of the migration. Since events don't really affect chain state, we would like to ignore them.

Not sure how to implement this, we could hardcode some known keys and ignore them in the state diff comparison, or simply allow users to pass some flag with a list of keys to ignore.

Issue では try-runtime ツール、その冪等性チェック、state diff の比較について言及されていますが、ファイルやテストは示されていません。まず、冪等性チェックの実装と state keys の比較方法を特定してください; users が events や eventsCount などの keys を無視するよう設定でき、他の mismatches を隠さない状態になれば完了です。