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

spec/javascripts/vue_shared/components/user_avatar_link_spec.js

 import Vue from 'vue';
 import UserAvatarLink from '~/vue_shared/components/user_avatar/user_avatar_link.vue';
-fdescribe('User Avatar Link Component', function () {
+describe('User Avatar Link Component', function () {
   beforeEach(function () {
     this.propsData = {
       href: 'myavatarurl.com',