fix(audit): create audit log for deleted conditions in a segment

[matthewelwell]

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• I have added information to docs/ if required so people know about the feature!
• I have filled in the "Changes" section below?
• I have filled in the "How did you test this code" section below?
• I have used a Conventional Commit title for this Pull Request

Changes

This PR solves an issue noticed in customer testing which showed that audit log records are not properly created when a condition is removed from a segment. The issue was caused by the following exception in the task processor:

...
  File "/Users/matthewelwell/projects/flagsmith/flagsmith/api/segments/models.py", line 206, in _get_project
    return self.rule.get_segment().project
           ^^^^^^^^^
  File "/Users/matthewelwell/projects/flagsmith/flagsmith/.venv/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 187, in __get__
    rel_obj = self.get_object(instance)
              ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/matthewelwell/projects/flagsmith/flagsmith/.venv/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py", line 154, in get_object
    return qs.get(self.field.get_reverse_related_filter(instance))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/matthewelwell/projects/flagsmith/flagsmith/.venv/lib/python3.11/site-packages/django/db/models/query.py", line 435, in get
    raise self.model.DoesNotExist(
segments.models.SegmentRule.DoesNotExist: SegmentRule matching query does not exist.

To resolve it, I have simply added soft delete to both the SegmentRule and Condition models.

How did you test this code?

This is really hard to test in unit test because it's essentially a race condition. It's very easy to test when using the Task Processor, however, so I have run the application locally with the task processor and verified the issue exists before then resolving it with the code here and retesting it locally to confirm that the issue no longer exists.

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Name	Status	Preview	Comments	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview		Mar 7, 2024 3:59pm
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flagsmith-frontend-staging	✅ Ready (Inspect)	Visit Preview		Mar 7, 2024 3:59pm

[github-actions]

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.86%. Comparing base (0080509) to head (bbfcfa6).
Report is 23 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3577   +/-   ##
=======================================
  Coverage   95.86%   95.86%           
=======================================
  Files        1097     1098    +1     
  Lines       34141    34145    +4     
=======================================
+ Hits        32728    32732    +4     
  Misses       1413     1413           

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