[mock-chronik-client] Remember to build before publishing

Summary: Published lib does work but only for ts users, because forgot to add build step to deployment. Add it. Update changelog.

Test Plan: docker build -f mock-chronik-client.Dockerfile -t mock-chronik-client_local .

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D17338