feat: ✨ Allow changing base url with Route.API_BASE_URL

[Paillat-dev]

Summary

Allows to change the base url e.g. if you wanna use canary. It's a very simple implementation idk if this would be enough to get merged.

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.

[Lulalaby]

good addition for testing new features easily

[Paillat-dev]

For reference, here is how to use:

import discord

discord.Route.API_BASE_URL = "https://canary.discord.com/api/v{API_VERSION}"