Drop dependency on django-database-locks

[DDuarte]

django-database-locks can still be used by implementations by subclassing the run_bot command

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.

Project coverage is 55.63%. Comparing base (e33242c) to head (55fb78c).
Report is 1 commits behind head on main.

Files	Patch %	Lines
slackbot/management/commands/run_bot.py	0.00%	23 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   55.23%   55.63%   +0.40%     
==========================================
  Files          10       10              
  Lines         277      275       -2     
==========================================
  Hits          153      153              
+ Misses        124      122       -2     

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud