Nomad service parsing silently "corrects errors" without failing

nomad version: 0.10.0

job extract:
```
job "presto" {
....
group "worker" {
count = 1
service {
port = "https"
connect {
sidecar_service {
proxy {
upstreams {
destination_name = "hive-connect-metastore"
local_bind_port = 9083
}
}
}
}
}
network {
mode = "bridge"
# This exposes a port externaly
port "https" {}
}
task "db" {
driver = "docker"
...
}
service {
name = "${NOMAD_JOB_NAME}-${NOMAD_GROUP_NAME}-${NOMAD_TASK_NAME}-${NOMAD_ALLOC_INDEX}"
connect {
sidecar_service {
proxy {
upstreams {
destination_name = "hive-connect-metastores"
local_bind_port = 9085
}
}
}
}
}
}
}
```

While getting to grips with nomad's consul connect implementation I came across this code path.
Edit: Which seemingly deletes the connect part?
https://github.com/hashicorp/nomad/blob/3e38891b88e089b57093efbdcbecd17fddaee001/jobspec/parse_service.go#L63
I copied the connect spec to a different task group, but instead of adding it to the group, I added it to a service stanza in the task. It took a good while to understand why none of my changes seemingly would take effect.

Expected outcome: An error message that connect stanzas are not allowed inside of a task.

- Edited to add context.

Start in jobspec/parse_service.go around the referenced line and inspect how a connect stanza inside a task service is handled. Reproduce the supplied job configuration, then verify that this misplaced stanza produces an error instead of being silently ignored or removed. Confirm the expected rejection using the repository's relevant job-spec parsing checks.

Written by the indexing model from the issue text.