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

@@ -109,13 +109,13 @@ gl.issueBoards.IssueCardInner = Vue.extend({
             {{ issueId }}
           </span>
         </h4>
-        <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 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>
       </div>