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/boards/components/issue_card_inner.js

@@ -109,15 +109,15 @@ gl.issueBoards.IssueCardInner = Vue.extend({
             {{ issueId }}
           </span>
         </h4>
-        <user-avatar-link v-if="assigneeUrl"
+        <user-avatar-link
+          v-if="assigneeUrl"
           class="card-assignee js-no-trigger"
           :href="assigneeUrl"
           :img-alt="avatarUrlTitle"
           :img-src="issue.assignee.avatar"
           :img-size="20"
-          :tooltip-text="issue.assignee.name">
-        </user-avatar-link>
-        </a>
+          :tooltip-text="issue.assignee.name"
+        />
       </div>
       <div class="card-footer" v-if="showLabelFooter">
         <button