[mock-chronik-client] Publish as npm pkg and install where used

Summary:
This library is used extensively enough, even if just internally, to merit publishing. This will simplify its use from different dir levels of the monorepo and also allow it to become more complex (i.e. use dependencies like ecashaddrjs).

While running regtest integrations is the "best" way to solve some testing problems, there is still a place for this as a dev tool.

Will move it to modules/ and set up automated npm publishing in later diffs.

Test Plan: CI will run npm test in impacted modules

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D15614