feat: implement purge command

[HeadTriXz]

Closes #21, part of #24.

• Adds /purge command.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (aa64863) 98.93% compared to head (e76844d) 98.94%.

Additional details and impacted files

@@           Coverage Diff            @@
##             main      #80    +/-   ##
========================================
  Coverage   98.93%   98.94%            
========================================
  Files         123      124     +1     
  Lines       15063    15203   +140     
  Branches     1595     1620    +25     
========================================
+ Hits        14903    15043   +140     
  Misses        160      160            

Flag	Coverage Δ
barry	98.56% <100.00%> (+0.01%)	⬆️
core	99.92% <ø> (ø)
logger	100.00% <ø> (ø)

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Files Changed	Coverage Δ
...dules/moderation/commands/chatinput/purge/index.ts	100.00% <100.00%> (ø)

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