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

@@ -9,7 +9,7 @@ export default {
   props: {
     href: {
       type: String,
-      required: false,
+      required: true,
     },
     imgSrc: {
       type: String,
@@ -18,22 +18,27 @@ export default {
     imgAlt: {
       type: String,
       required: false,
+      default: '',
     },
     imgCssClasses: {
       type: String,
       required: false,
+      default: '',
     },
     imgSize: {
       type: Number,
       required: false,
+      default: 20,
     },
     tooltipText: {
       type: String,
       required: false,
+      default: '',
     },
     tooltipPlacement: {
       type: String,
       required: false,
+      default: '',
     },
   },
 };