feature request: Exclude `/` also from job names

### Proposal
The proposal is to disallow slash `/` from job names.

### Use-cases
The use case is to use `job/group/task` format when referencing a task in a group within a job. Currently, job names are allowed to contain slashes, but group and task names are not. I think it would be great to also disallow task names to contain slashes, for easier referencing without any escaping. It would also make easier to make HTTP requests, where `/` is the URL parts separator.

### Attempted Solutions
The solution, like in the case of nomad web UI, is to visually distinguish job name from the separator. Another is to escape `\/` slash like in `sed`.

Start by tracing Nomad's validation and HTTP reference paths for job, group, and task names. Confirm whether the requested restriction applies to job names, task names, or both, then define tests showing slash-free names work with job/group/task references and HTTP requests.

Written by the indexing model from the issue text.