[CI] Run the chronik-client unit tests on diffs

Summary:
Similar to other build configs, this will trigger and run the unit tests each time a file under modules/chronik-client/ is touched, and generate a coverage report.
This requires the addition of a couple dev dependencies to install the mocha plugins required for proper CI reporting.

Test Plan:

./contrib/teamcity/build-configurations.py chronik-client-tests

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14445