* backend: makes mongo auth configurable!
use mongo_auth secret in k8s and set env vars in docker
fixes#177
* docker: update config.sample.env: use ws screencast by default, add NO_DELETE_ON_FAIL option, extend default login lifetime
- set WEB_CONCURRENCY env var to configure number of backend api workers for both docker and k8s
- set via 'backend_workers' in values.yaml
- also add 'rwp_base_url' to values.yaml
- update containers to use public webrecorder/browsertrix-backend and webrecorder/browsertrix-frontend containers
- make liveness, readiness and startup health checks more tolerant
