Consolidate user avatar Vue logic

Creates 3 vue components:

1. user-avatar-link
2. user-avatar-image
3. user-avatar-svg

and implements them in several places.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/31017

• Port to EE
• Test each implementation manually

EE Compatible Branch: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1699

app/assets/javascripts/diff_notes/components/diff_note_avatars.js

@@ -3,7 +3,7 @@
 import Vue from 'vue';
 import collapseIcon from '../icons/collapse_icon.svg';
-import UserAvatarImage from '../vue_shared/components/user_avatar/user_avatar_image';
+import UserAvatarImage from '../../vue_shared/components/user_avatar/user_avatar_image';
 const DiffNoteAvatars = Vue.extend({
   props: ['discussionId'],