feat: implement Avatar Decorations

[NeloBlivion]

Summary

Better late than never...?
There seems to be several different endpoints, so I've tried to include them.
Despite no longer being available, you can still get any user's decoration.
Unlike banners, User.avatar_decoration is always received without needing to fetch the user.

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.

[codecov]

Codecov Report

Merging #2131 (fe0d2f7) into master (ca2f5da) will decrease coverage by 0.01%.
The diff coverage is 30.76%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2131      +/-   ##
==========================================
- Coverage   33.88%   33.88%   -0.01%     
==========================================
  Files         109      109              
  Lines       22343    22356      +13     
==========================================
+ Hits         7571     7575       +4     
- Misses      14772    14781       +9     

Flag	Coverage Δ
macos-latest-3.10	33.86% <30.76%> (-0.01%)	⬇️
macos-latest-3.11	33.86% <30.76%> (-0.01%)	⬇️
macos-latest-3.8	33.86% <30.76%> (-0.01%)	⬇️
macos-latest-3.9	33.86% <30.76%> (-0.01%)	⬇️
ubuntu-latest-3.10	33.86% <30.76%> (-0.01%)	⬇️
ubuntu-latest-3.11	33.86% <30.76%> (-0.01%)	⬇️
ubuntu-latest-3.8	33.86% <30.76%> (-0.01%)	⬇️
ubuntu-latest-3.9	33.86% <30.76%> (-0.01%)	⬇️
windows-latest-3.10	33.86% <30.76%> (-0.01%)	⬇️
windows-latest-3.11	33.86% <30.76%> (-0.01%)	⬇️
windows-latest-3.8	33.86% <30.76%> (-0.01%)	⬇️
windows-latest-3.9	33.86% <30.76%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
discord/user.py	36.84% <25.00%> (-0.48%)	⬇️
discord/asset.py	38.77% <40.00%> (+0.04%)	⬆️

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[OmLanke]

discord/discord-api-docs#5723 got merged. This can too?

[Lulalaby]

On hold till adc rolls out

[Dorukyum]

On hold till adc rolls out

@Lulalaby update?

[Lulalaby]

There have been some recent changes. Imma look this week

[Lulalaby]

lets finish that up

[NeloBlivion]

Decorations haven't changed much, apart from one thing; we now recieve a dict avatar_decoration_data instead:

{'asset': 'a_c7e1751e8122f1b475cb3006966fb28c', 'sku_id': '1154896005045694555'}

The asset ID is all we really need, does sku_id serve any purpose from a bot perspective? At the moment we still save that entire dict under User._avatar_decoration.