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/vue_shared/components/user_avatar/user_avatar_link.vue

 <script>
 import userAvatarImage from './user_avatar_image.vue';
-import userAvatarSvg from './user_avatar_svg';
 export default {
   name: 'UserAvatarLink',
   components: {
     userAvatarImage,
-    userAvatarSvg,
   },
   props: {
     href: {
@@ -54,4 +52,4 @@ export default {
       :tooltip-placement="tooltipPlacement"
     />
   </a>
-</template>
\ No newline at end of file
+</template>