Allow middleware access to job queue

[adam-fowler]

One of the limitations of job middleware was it wasn't possible to construct a middleware that held the job queue. This PR resolves this by providing a separate initialiser for JobQueue which passes the queue driver to the closure that constructs the middleware chain.

let jobQueue = JobQueue(.memory, logger: logger) { queue in
    TestMiddleware(queue: queue)
}

For instance this could be used to create a middleware that sets metadata on job completion

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.39%. Comparing base (93d35fd) to head (458715a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #123      +/-   ##
==========================================
+ Coverage   86.81%   87.39%   +0.57%     
==========================================
  Files          25       25              
  Lines        1320     1325       +5     
==========================================
+ Hits         1146     1158      +12     
+ Misses        174      167       -7     

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