[Cashtab] Update param parsing function to support opreturn param

Summary:
Cashtab currently only supports the amount param.

Update parseAddressForParams function to also support the opreturn param.

Ref proof of concept D15032

Note: this diff does not yet implement the ability to create and broadcast txs using this param, although it does update a function currently implemented on the Send.js screen. This diff does not break existing amount functionality. For now, if a valid opreturn param is in a query string, it is ignored.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15075