Use a priority queue

[p-j-smith]

Description

Fixes #472: Use a priority queue to allow for high priority populating of studies

• set "x-max-priority": 5 when creating a queue (the value recommended in RABBITMQ docs for priority queues). Higher values are higher priority
• add --priority argument to the populate cli command for setting the priority of messages
• update tests to set priority of messages
• update docs to explain how to set the priority of messages

Type of change

Please delete options accordingly to the description.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Suggested Checklist

• [ ] I have performed a self-review of my own code.
• [ ] I have made corresponding changes to the documentation.
• [ ] My changes generate no new warnings.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have passed on my local host device. (see further details at the CONTRIBUTING document)
• [ ] Make sure your branch is up-to-date with main branch. See CONTRIBUTING for a general example to syncronise your branch with the main branch.
• [ ] I have requested PR review to UCLH-Foundtry/arc-dev
• [ ] I have adddressed and marked as resolved all the review comments in my PR.
• [ ] Finally, I have selected squash and merge

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.79%. Comparing base (ba6e174) to head (34255cb). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cli/src/pixl_cli/main.py	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #499 +/- ## ======================================= Coverage 85.78% 85.79% ======================================= Files 86 86 Lines 3990 3991 +1 ======================================= + Hits 3423 3424 +1 Misses 567 567 ```

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