[chronik] Python client: add support for paths in host

Summary:
So we can support hosts that look like so: https://chronik.foo/xec

We don't use that in tests but it is useful for external scripts relying on this library.

Test Plan: Use it to connect to the public chronik.pay2stay.com/xec

Reviewers: #bitcoin_abc, tobias_ruck

Reviewed By: #bitcoin_abc, tobias_ruck

Subscribers: tobias_ruck

Differential Revision: https://reviews.bitcoinabc.org/D18480