[Cashtab] [chronik tx history p6] Detect OP_RETURN msgs and run through existing parse function

Summary:
T2447

Depends on D12054

Detect OP_RETURN msgs from chronik data. Run msg through existing parseOpReturn(hex) function.

Fully parsing the msgs will be done in a later diff on this stack.

Test Plan:
npm start

Send some OP_RETURN msgs. Confirm parsedOpReturnArray in dev console lines up, i.e. check for Cashtab msg prefix.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12056