Change metadata label to u64 once supported by sqlx / sea-orm

[SebastienGllmt]

Currently sqlx (and therefore sea-orm) doesn't support u64 (aka bit int unsigned) for Postgres, which means instead we have to use bytea which isn't ideal.

We should replace this if/when this is ever supported https://github.com/dcSpark/carp/blob/9e434bbe87d4d6ab496a23045412a6c5a891c569/indexer/entity/src/transaction_metadata.rs#L10