[Enhancement] Support Geyser (bedrock players) for webhook avatars

[str0bi]

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Description

The Discord webhook that adds avatars to players' messages currently shows Bedrock players (through Geyser/Floodgate) as Steve. Would be nice to see it work with their skins as well :)

[Xujiayao]

Seems that there is currently no public online skin API that supports getting skins for a Bedrock account 🤔

[Xujiayao]

Please use the latest build.

Support Geyser and all real-time skin replacement mods/plugins.

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The new default value of avatarApi is this:

"avatarApi": "https://mc-heads.net/avatar/{player_uuid}.png",

If you want it to support real-time skin replacement mods/plugins or Geyser, you should change its value to the following:

"avatarApi": "https://mc-heads.net/avatar/{player_textures}.png",

I may change the default to {player_textures} before releasing the new version, or even consider rename avatarApi to avatar_url.