[query-api] Use string for txID

[liran-funaro]

Unrelated to this PR. Given that txID is string in fabric, we can change this to string itself in a separate PR. Otherwise, the clients have to do the same unnecessarily.

Originally posted by @cendhu in hyperledger/fabric-x-committer#341 (comment)

[cynox-66]

Hey @liran-funaro , I took a closer look at this and noticed the proto in fabric-x-common already uses string tx_id.

From what I can see, the remaining []byte usage is in fabric-x-committer, including the tx_status table where tx_id is stored as BYTEA.

So fixing this properly would likely involve changing the DB schema + updating the Go code, not just a small change here.

Just wanted to check — is the expectation to handle this fully in committer (including schema), or keep it scoped somehow?