Run the CT suite in CI and replace thoas with OTP json #34

Two follow-ups from the review of #33:

• CI runs compile, dialyzer, xref and lint only. The 12 CT tests need a Postgres service, a running chatli node and the demo seed (etsi103707demo/seed/seed.sql, get_all_users expects 3 seeded users + 2 signups - self). Add a postgres service, boot the app, seed, rebar3 ct. Consider moving to the Taure/erlang-ci reusable workflow at the same time.
• thoas is used directly in src and test but declared nowhere; it arrives transitively through nova 0.16 and Nova 1.0 drops it. Migrate to OTP json.