feat(client): implement new entitlement endpoint and parameter

[Snipy7374]

Summary

• Closes implement new entitlement endpoint #1249

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• 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, ...)

[shiftinv]

since Client.entitlements is also new in 2.10, the addition of exclude_deleted in the same version doesn't have to be mentioned here.

It would be awesome if you could merge the Client.fetch_entitlement part with the other two changelog fragments for entitlements (1113 + 1186), such that all entitlement changes are grouped in the final changelog.
For instance, 1113.feature.rst and 1186.feature.rst already have the same content, so towncrier shows them as one entry with both PR numbers¹:

Footnotes

1. (this feature is a bit weird, but that's just how towncrier works; let me know if anything's confusing) ↩

[shiftinv]

Looks like the new exclude_deleted parameter defaults to true (unlike exclude_ended), we should reflect that here as well: discord/discord-api-docs@e6ac32c#diff-82a22117a97948da6ec935f7b23f3bec7a1d6b4cef7119bb5610d92b95fbeb86R76