feat(SlashCommandBuilder): create setDefaultPermission function

[Fyko]

Please describe the changes this PR makes and why it should be merged: This PR creates SlashCommandBuilder#setDefaultPermission.

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating
• This PR changes the library's interface (methods or parameters added)

[codecov-commenter]

Codecov Report

Merging #19 (dd45da5) into main (2aecbe4) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #19   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           15        16    +1     
  Lines          144       147    +3     
  Branches        21        17    -4     
=========================================
+ Hits           144       147    +3     

Impacted Files	Coverage Δ
src/interactions/slashCommands/Assertions.ts	100.00% <100.00%> (ø)
.../interactions/slashCommands/SlashCommandBuilder.ts	100.00% <100.00%> (ø)
...nteractions/slashCommands/mixins/CommandOptions.ts	100.00% <0.00%> (ø)
...s/slashCommands/mixins/CommandOptionWithChoices.ts	100.00% <0.00%> (ø)
src/interactions/slashCommands/options/number.ts	100.00% <0.00%> (ø)

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