feat: add interface to expose HTTP ports on batch jobs

[mortenpi]

The exact API is still WIP, and needs tests and more docs, but adds two functions right now:

First, an expose argument to JuliaHub.submit_job, that allows you to specify that a port from the job container should be exposed, e.g.:

JuliaHub.submit_job(
    JuliaHub.appbundle(@__DIR__, "run.jl"),
    expose=8080
)

It also adds a JuliaHub.request function that takes a JuliaHub.Job as an argument and constructs a HTTP.request (pretty much a wrapper around HTTP.request; close #14):

julia> myjob = JuliaHub.job("jr-jgz2xmxas6");

julia> JuliaHub.request(myjob, "GET", "/")
HTTP.Messages.Response:
"""
HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
Content-Length: 12
Connection: keep-alive
Server: openresty
Date: Fri, 24 May 2024 07:44:59 GMT
Expires: Fri, 24 May 2024 07:45:00 GMT
Cache-Control: max-age=1, no-cache

hello world!"""

[pfitzseb]

Should we allow for ::Nothing or similar here as well? To allow for "anonymous" access, basically.

[mortenpi]

In my opinion, we should only do that once we have the API to submit jobs that allow for anonymous access, otherwise it's not really consistent between the two functions. I like the API idea itself though (i.e. using nothing for that).

[mortenpi]

Also, the function is a very thin wrapper around HTTP.request. So if you do want to make unauthenticated requests, you can just get the hostname from job.hostname and call HTTP.request yourself.