feat!: adjust webhook methods to match latest discord api docs

[DevYukine]

Description

This PR adjusts webhook.go with following changes:

• Removes Execute methods on WebhookQueryBuilder (interface & impl) because these methods will not work without token and the current implementation just sets token to "" which will always return a Missing Token Error (no need to keep functions which always error)
• Adds missing Execute (ExecuteGithub/ExecuteSlack) functions to WebhookWithTokenQueryBuilder struct
• Add missing Get/Edit/Delete Message functions to WebhookWithTokenQueryBuilder struct
• Adjust Execute definition to make wait & threadId fully optional as by Discord Docs
• Adjust execWebhook for the optional values
• Replaced deprecated errors with non deprecated ones

I've also run go generate once to regenerate anything needed, i hope that was right as the readme just briefly mentions this but not say if this is required or not on PRs

Breaking Change?

yes

Benchmarks

Checklist:

• I have performed a self-review of my own code
• Commented complex situations or referenced the discord documentation
• Updated documentation
• Added/Updated unit tests
• Added/Updated benchmarks (if this is a performance critical component)

[andersfylling]

I'll take a look this weekend. I'm a bit occupied today.

[andersfylling]

LGTM!