Health and readiness handlers.

live/0 is a liveness probe - it always answers 200 {"status":"ok"} (the process is up). ready/1 is a readiness probe - it runs a list of named checks and answers 200 when all pass, or 503 listing the failed checks. Mount them on routes:

R1 = livery_router:add('GET', <<"/healthz">>, livery_health:live(), #{}, R0),
R2 = livery_router:add(
    '_GET', <<"/readyz">>,
    livery_health:ready([{<<"db">>, fun () -> my_db:ping() end}]),
    #{}, R1
).

A check is {Name, fun(() -> ok | {error, term()})}; any non-ok return or a raised exception counts as failed. Checks run synchronously in the request process, so keep them fast.