fix: Document Option.channel_types and properly support further channel types

[NeloBlivion]

Summary

• Finally documents discord.Option.channel_types
• Allows input_type to accept discord.ForumChannel and discord.DMChannel.
  Ref. discord.ForumChannel Bug #1882
• channel_types now overrides the input_type

Information

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed).
• This PR is not a code change (e.g. documentation, README, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.

[NeloBlivion]

So some clarification

1. channel_types only worked if you use discord.SlashCommandOptionType.channel, not standard channel classes (as pointed out in the linked issue)
2. For some reason, the Discord API actually allows private channels as an option type

Thus changes:

1. Now channel_types will override the input_type's ChannelType
2. Both discord.ForumChannel and discord.DMChannel are now supported for input_type

Though I can see these some of this being questionable, so do give your thoughts.

[codecov]

Codecov Report

Merging #1883 (192a086) into master (9da7cf9) will decrease coverage by 0.01%.
The diff coverage is 33.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1883      +/-   ##
==========================================
- Coverage   33.27%   33.26%   -0.01%     
==========================================
  Files          96       96              
  Lines       18695    18696       +1     
==========================================
  Hits         6220     6220              
- Misses      12475    12476       +1     

Flag	Coverage Δ
macos-latest-3.10	33.25% <33.33%> (-0.01%)	⬇️
macos-latest-3.11	33.25% <33.33%> (-0.01%)	⬇️
macos-latest-3.8	33.26% <33.33%> (-0.01%)	⬇️
macos-latest-3.9	33.26% <33.33%> (-0.01%)	⬇️
ubuntu-latest-3.10	33.25% <33.33%> (-0.01%)	⬇️
ubuntu-latest-3.11	33.25% <33.33%> (-0.01%)	⬇️
ubuntu-latest-3.8	33.26% <33.33%> (-0.01%)	⬇️
ubuntu-latest-3.9	33.26% <33.33%> (-0.01%)	⬇️
windows-latest-3.10	33.25% <33.33%> (-0.01%)	⬇️
windows-latest-3.11	33.25% <33.33%> (-0.01%)	⬇️
windows-latest-3.8	33.26% <33.33%> (-0.01%)	⬇️
windows-latest-3.9	33.26% <33.33%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
discord/enums.py	79.61% <ø> (ø)
discord/commands/options.py	16.55% <33.33%> (-0.12%)	⬇️

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