service discovery: allow setting and discovering meta and canary_meta fields in Nomad services

Nobody has claimed this yet.

Allow setting [meta](https://www.nomadproject.io/docs/job-specification/service#meta) and [canary_meta](https://www.nomadproject.io/docs/job-specification/service#canary_meta) parameters on services using the `nomad` provider. It is possible that external tooling uses these fields for discovery and routing alongside tags. The [Nomad Ingress NGINX pack](https://github.com/hashicorp/nomad-pack-community-registry/tree/main/packs/nomad_ingress_nginx) showcases this.

There is a bug within the current code that allows a job to be registered that includes a nomad service with `meta` and `meta_canary` fields. The fields are persisted within the job specification, but do not make it to the service registration.

Example job spec:
```
job "example" {
datacenters = ["dc1"]

group "cache" {
network {
port "db" {
to = 6379
}
}

service {
provider = "nomad"
port = "db"
meta {
foo = bar
}
}

task "redis" {
driver = "docker"

config {
image = "redis:3.2"
ports = ["db"]
}
}
}
}
```

Start by tracing the Nomad provider's service registration path from the job specification, focusing on how meta and canary_meta are persisted and then passed to registration. Compare the job fields with the registered service fields; done means both metadata fields are discoverable on services, including the example configuration.

Written by the indexing model from the issue text.