Refactor get prs

[khalford]

Re-Write of the GitHub pull request collection functionality.

Moved JSON request data serialisation into the dataclass itself.
Checking for stale pull requests after collecting them.
Option to sort pull requests by properties

[codecov]

Codecov Report

Attention: Patch coverage is 99.25373% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.89%. Comparing base (fe0e2b2) to head (dd2e9c8).

Files with missing lines	Patch %	Lines
cloud-chatops/tests/test_find_prs.py	97.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #75      +/-   ##
==========================================
- Coverage   96.25%   95.89%   -0.36%     
==========================================
  Files          19       19              
  Lines         802      756      -46     
==========================================
- Hits          772      725      -47     
- Misses         30       31       +1     

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