[chronik-client] Support raw-tx endpoint in ChronikClientNode

Summary:
Add support for the raw-tx endpoint.

I overlooked that this endpoint existed in my first pass of getting this to work. This should have been included with blocktxs and txs, imo closely related.

Use the same test script.

Test Plan: See test plan from D14915 or let CI handle it.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15350