Expose Consul health check identifier

We want to use Nomad together with Consul. One of our libraries registers a session with Consul and adds additional checks (serf and service). The Consul API is not very specific about it but it looks from observed behavior that the checks are actually IDs of checks (https://www.consul.io/api/session.html#checks).

Our current implementation does not use Nomad. It registers checks manually on Consul and it sets the ID which is then used by the library. The Consul API permits that (https://www.consul.io/docs/agent/checks.html).

When running with Nomad the ID of the Consul check is generated. Hence the library doesn't know it. I would like to set the ID of the check - currently Nomad does not allow that: https://www.nomadproject.io/docs/job-specification/service.html#check-parameters

Alternatively, since I set the ID of the additional check as an env variable, if Nomad exports the generated value in some way I can use that.

Start with Nomad's service check parameters and the Consul session and agent check API documentation linked in the issue. Define whether completion means accepting an explicit Consul check ID or exposing Nomad's generated ID, then trace the service registration path and add coverage for the selected behavior.

Written by the indexing model from the issue text.