fix: premium buttons and entitlement iterator

[tibue99]

Summary

This PR fixes some issues with monetization.

1) Premium buttons do not work with a custom ID, I disabled the auto-generated custom_id for premium buttons 2) bot.fetch_entitlements() did not work when certain parameters were not set 3) The exclude_ended attribute threw an error, because yarl does not support boolean params. I don't know how to fix that, so I just set it to None for now. Perhaps @plun1331 can help

I have tested the changes with a monetized Discord bot.

Edit: This PR now renames client.fetch_entitlements to client.entitlements.

Information

• [x] 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

• [x] I have searched the open pull requests for duplicates.
• [x] 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.

[plun1331]

The exclude_ended attribute threw an error, because yarl does not support boolean params. I don't know how to fix that, so I just set it to None for now. Perhaps @plun1331 can help

Casting it to a string in the http method should be good enough

Edit: other methods have cast it to int

[Lulalaby]

Timo for the win. Thank you

[Dorukyum]

Have the latest changes been tested?

[tibue99]

Have the latest changes been tested?

I have tested client.entitlements() in production, but I have not tested the user/guild methods separately.