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

@@ -153,7 +153,7 @@ gl.issueBoards.IssueCardInner = Vue.extend({
           <user-avatar-link
             v-for="(assignee, index) in issue.assignees"
             v-if="shouldRenderAssignee(index)"
-            class="card-assignee js-no-trigger"
+            class="js-no-trigger"
             :link-href="assigneeUrl(assignee)"
             :img-alt="avatarUrlTitle(assignee)"
             :img-src="assignee.avatar"