create /healthcheck and /metrics endpoints in workers
fixes #2067

- [x] Publish /metrics and /healthcheck endpoints in workers
- [x] Check worker's health with the new endpoint
- [x] Fetch worker's Prometheus metrics
- [x] Instrument parts of the worker's code
create /healthcheck and /metrics endpoints in workers: fixes #2067

- [x] Publish /metrics and /healthcheck endpoints in workers
- [x] Check worker's health with the new endpoint
- [x] Fetch worker's Prometheus metrics
- [x] Instrument parts of the worker's code