satellite/audit: create the audit queue

[navillasa]

What:

• adds an audit queue containing paths to audit
• adds worker method to ReservoirService to do audit jobs (that is, auditing paths on the queue)

Why:

• To create clearer organization of the audit system--
  • reservoirChore.Run adds reservoir paths to queue in pseudorandom order
  • audit workers will take a path from the queue and run an audit on that path
  • no duplicate paths will be added to the queue
  • paths will be deleted from the queue as soon as an audit worker picks up the path
  • the random selection from the reservoirs (in pr satellite/audit: random path selection #2861) was a bit convoluted

Please describe the tests:

• TestChoreAndWorkerIntegration:
  This test ensures that after uploading 2 files (1 remote segment each), the paths for those files appear appropriately in the queue.

• TestQueue:
  This tests the expected behavior of the Swap and Next methods of the queue struct.

Please describe the performance impact:

Code Review Checklist (to be filled out by reviewer)

• Does the PR describe what changes are being made?
• Does the PR describe why the changes are being made?
• Does the code follow our style guide?
• Does the code follow our testing guide?
• Is the PR appropriately sized? (If it could be broken into smaller PRs it should be)
• Does the new code have enough tests? (every PR should have tests or justification otherwise. Bug-fix PRs especially)
• Does the new code have enough documentation that answers "how do I use it?" and "what does it do?"? (both source documentation and higher level, diagrams?)
• Does any documentation need updating?
• Do the database access patterns make sense?

[egonelbre]

Few nits, but otherwise looks good.

[egonelbre]

nit: Let's keep the config organised the same way as the definition.

[egonelbre]

This can be written as:

for _, expected := range testQueue2 {
    path, err := q.Next()
    require.NoError(t, err)
    require.EqualValues(t, expected, path)
}

[egonelbre]

If the other audit thing is going away, this could be named just Chore, because there wouldn't be a naming conflict.

[ifraixedes]

I think that's worth to wait for @mobyvb review