Include LogEntry instance in post_log signal

[ppmathis]

Thank you for maintaining this great project! While working on a specific use case where I wanted to further process audit messages, I stumbled across the fact that the post_log signal which has been introduced in v3 somehow does not contain the actual instance of the LogEntry that has been created and saved.

This was rather confusing to me and makes it impossible to implement my use case, which also requires access to fields like cid, remote_addr, timestamp or actor - for the latter I even found an open issue #576 on this repository, where a user was also missing the possibility to access the actor of a LogEntry.

While all kinds of fields could be added to the signal, I hereby propose to simply pass the actual LogEntry instance as part of the signal when available, which I deem a simpler solution and avoids adding more and more arguments to the signal. This PR adds the log_entry argument, which is either an instance of LogEntry (= changes made/force-log and persisted) or None (= error occurred).

This will allow easily accessing all the available model fields in a signal or even directly interacting with the specific LogEntry instance in other ways. Merging this PR would fix #576 as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1ce39c0) 95.20% compared to head (21e6add) 95.20%.
Report is 1 commits behind head on master.

Additional details and impacted files

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- Coverage   95.20%   95.20%   -0.01%     
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  Files          31       31              
  Lines        1022     1021       -1     
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- Hits          973      972       -1     
  Misses         49       49              

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[hramezani]

Thanks @ppmathis