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

@@ -159,7 +159,7 @@ gl.issueBoards.IssueCardInner = Vue.extend({
             :img-src="assignee.avatar"
             :img-size="20"
             :tooltip-text="assigneeUrlTitle(assignee)"
-            :tooltip-placement="bottom"
+            :tooltip-placement="'bottom'"
           />
           <span
             class="avatar-counter has-tooltip"