Expose TxID on a cadidate TX

[Yoav Tock]

Expose TxID on the DataTxContext object (as well as config, db, user).

Use case from @liran-funaro , some time we want to use the tx-id in the data itself, e.g. create keys that are unique to the TX.

Add to type TxContext interface a function
TxID() string which returns the txid created when the DataTxContext was created.

look at

orion-sdk-go/pkg/bcdb/db.go

Line 51 in d4680bb

 type TxContext interface {