Store commit ID (transaction ID) in metadata

[swistak35]

If it's available, it can be worth it to store commit ID (or "transaction id") in event's metadata, in order to know which events were published in one transaction, as a whole.

It probably would need some RubyEventStore support, but the core of that feature would be for the Repository to actually provide transaction ID. That can be used alongside for example with building read models or other DB transactions, to see which changes were grouped together.

(note from one of KanDDDinsky talks, I don't remember which one -- I think Dennis Doomen's one, about projections)