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/cycle_analytics/components/stage_code_component.js

@@ -23,6 +23,7 @@ global.cycleAnalytics.StageCodeComponent = Vue.extend({
       <ul class="stage-event-list">
         <li v-for="mergeRequest in items" class="stage-event-item">
           <div class="item-details">
+            // FIXME: Pass an alt attribute here for accessibility
             <user-avatar-image :src="mergeRequest.author.avatarUrl"/>
             <h5 class="item-title merge-merquest-title">
               <a :href="mergeRequest.url">