Add update avatar on user api

What does this MR do and why?

Add Update avatar on user api

Endpoint: user/avatar

This MR allows users to customize avatars for group and project access token bots.

Connected to : Allow avatar customization for group or project... (#356868 - closed)

How to set up and validate locally

curl --request PUT \
  --url http://gdk.test:3000/api/v4/user/avatar \
  --header 'Authorization: Bearer <PROJECT_OR_GROUP_BOT_ACCESS_TOKEN' \
  --header 'Content-Type: multipart/form-data' \
  --form 'avatar=@<PATH_TO_FILE>'

doc/api/users.md

@@ -2546,6 +2546,8 @@ Example response:
 
 ## Upload a current user avatar
 
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/148130) in GitLab 17.0.
+
 Upload an avatar to current user.
 
 ```plaintext
@@ -2615,5 +2617,4 @@ Returned object:
   "extra_shared_runners_minutes_limit": null,
   "scim_identities": []
 }
-{
 ```