feat(bot): allow separate member avatars for proxied messages (#523)

This allows for using one avatar for the member card, and a different
avatar for proxied messages - so that users can set the main avatar to
a "full" version of their avatar, and the "proxy" avatar to a cropped
version.

docs/content/api/models.md

@@ -46,6 +46,7 @@ Every PluralKit entity has two IDs: a short (5-character) ID and a longer UUID.
 |birthday|?string|`YYYY-MM-DD` format, 0004 hides the year|
 |pronouns|?string|100-character-limit|
 |avatar_url|?string|256-character limit, must be a publicly-accessible URL|
+|webhook_avatar_url|?string|256-character limit, must be a publicly-accessible URL|
 |banner|?string|256-character limit, must be a publicly-accessible URL|
 |description|?string|1000-character limit|
 |created|?datetime||

docs/content/command-list.md

@@ -65,6 +65,7 @@ Some arguments indicate the use of specific Discord features. These include:
 - `pk;member <member> servername <new server name>` - Changes the display name of a member, only in the current server.
 - `pk;member <member> description [description]` - Changes the description of a member.
 - `pk;member <member> avatar [avatar url|@mention|upload]` - Changes the avatar of a member.
+- `pk;member <member> proxyavatar [avatar url|@mention|upload]` - Changes the avatar used for proxied messages sent by a member.
 - `pk;member <member> serveravatar [avatar url|@mention|upload]` - Changes the avatar of a member in a specific server.
 - `pk;member <name> banner [image url|upload]` - Changes the banner image of a member.
 - `pk;member <member> privacy` - Displays a members current privacy settings.

docs/content/user-guide.md

@@ -229,6 +229,13 @@ To preview the current avatar (if one is set), use the command with no arguments
     
 To clear your avatar, use the subcommand `avatar clear` (eg. `pk;member John avatar clear`).
 
+### Member proxy avatar
+If you want your member to have a different avatar for proxies messages than the one displayed on the member card, you can set a proxy avatar. To do so, use the `pk;member proxyavatar` command, in the same way as the normal avatar command above:
+
+    pk;member John avatar
+    pk;member John proxyavatar http://placebeard.it/512.jpg
+    pk;member "Craig Johnson" proxyavatar    (with an attached image)
+
 ### Member server avatar
 You can also set an avatar for a specific server. This will "override" the normal avatar, and will be used when proxying messages and looking up member cards in that server. To do so, use the `pk;member serveravatar` command, in the same way as the normal avatar command above: