[chronik-client] Add existing package to the monorepo as-is

Summary:
Adding chronik-client to the monorepo as a preliminary step before adding mock-chronik-client into its codebase.

mock-chronik-client and chronik-client should exist in the same repo because both will need to be modified at the same time as new features are added.

Also, as chronik becomes more critical to the eCash infra stack, its tools should be maintained in the monorepo.

Test Plan: This diff was created by cloning https://github.com/givelotus/bitcoinsuite/tree/master/chronik-client into the modules/ folder of the monorepo. Review to confirm nothing obvious needs to be removed. Otherwise, monorepo functionality like linting, unit test ci, etc will be added later.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13776