Nomad Read Job API does not allow for querying * namespaces

### Nomad version
Nomad v1.0.4+ent

### Issue

The nomad api for [reading jobs](https://www.nomadproject.io/api-docs/jobs#read-job) does not allow for queries of jobs within the [AllNamespacesNamespace](https://github.com/hashicorp/nomad/blob/41a43a98dc82486d5524ba9b48597b1758ba339e/api/api.go#L35).

### Reproduction steps

`curl http://localhost:4646/v1/job/?namespace=*` will output `job not found`. So either I have to rely on the `default` namespace or I have to actually specify the exact name of the namespace my job lives in within the query. It would be easier if I could use the * for this query similar to the list job endpoint works.

Start with the read-job API endpoint described in the issue and the referenced api/api.go definition, then reproduce the behavior with the provided curl request using namespace=*. Done means a job can be read through the wildcard namespace query, with existing exact-namespace behavior preserved.

Written by the indexing model from the issue text.