feat: implement welcomer

[HeadTriXz]

Closes #46.

Implements a rather basic, yet customizable, welcomer feature. Might get changed in the future (custom image generation), but works fine for now.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (689520d) 99.07% compared to head (c028648) 99.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
+ Coverage   99.07%   99.08%   +0.01%     
==========================================
  Files         175      179       +4     
  Lines       18098    18437     +339     
  Branches     1947     1993      +46     
==========================================
+ Hits        17930    18268     +338     
- Misses        168      169       +1     

Flag	Coverage Δ
barry	98.82% <99.67%> (+0.01%)	⬆️
core	99.92% <ø> (+<0.01%)	⬆️
logger	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
apps/barry/src/Application.ts	100.00% <100.00%> (ø)
...es/welcomer/database/WelcomerSettingsRepository.ts	100.00% <100.00%> (ø)
apps/barry/src/modules/welcomer/database/index.ts	100.00% <100.00%> (ø)
...arry/src/modules/welcomer/events/guildMemberAdd.ts	100.00% <100.00%> (ø)
apps/barry/src/modules/welcomer/index.ts	100.00% <100.00%> (ø)
apps/barry/src/index.ts	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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