feat: ✨ Add fetch_roles_member_counts method to Guild and corresponding HTTP route

[Paillat-dev]

Summary

depends on discord/discord-api-docs#8021

Ref: https://discord.com/channels/881207955029110855/1411737823635312693/1446851187625164827

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.

[pycord-app]

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pip install git+https://github.com/Pycord-Development/pycord@refs/pull/3020/head