feat(commands): add support for typing.Literal[...] as command choices

[Lumabots]

Summary

permit the usage of choice like so :

@bot.command()
async def test(ctx: discord.ApplicationContext, test: Literal["1", "2"]): ...

instead of needed to do

@bot.command()
@discord.option(name="test", choices=["1", "2"])
async def test(ctx: discord.ApplicationContext, test: ...

or

@bot.command()
async def test(ctx: discord.ApplicationContext, test: discord.Option(str, choices=["1", "2"])): ...

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.
• I have updated the changelog to include these changes.

[VincentRPS]

LGTM

[VincentRPS]

LGTM

[Paillat-dev]

I approve the concept, I don't have time to read the code

[Lumabots]

does this need something else before being merged ?