Add a class to handle EvenLists

[jose-caballero]

Add a class with the required methods to handle the EventList for a given OpenStack Server.

Each instance should be instantiated for a given Server, or fail if that Server does not exist.

This class will be used to find out relevant information about the status of the Servers, which can help with future st2 Actions.

Description:

Special Notes:

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Submitter:

Have you (where applicable):

• Added unit tests?
• Checked the latest commit runs on Dev?
• Updated the example config file(s) and README?

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Reviewer

Does this PR:

• Place non-StackStorm code into the lib directory?
• Have unit tests for the action/sensor and lib layers?
• Have clear and obvious action parameter names and descriptions?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.19%. Comparing base (60fc4ec) to head (f16f92e).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #452   +/-   ##
=======================================
  Coverage   99.18%   99.19%           
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  Files         111      112    +1     
  Lines        2698     2726   +28     
  Branches      338      338           
=======================================
+ Hits         2676     2704   +28     
  Misses         19       19           
  Partials        3        3           

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