feat: update banner design [CW-1491] (#7296)

* refactor: banner styling

* refactor: update button style for reply assign banner

* feat: remove update-banner classes

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Co-authored-by: Nithin David Thomas <1277421+nithindavid@users.noreply.github.com>

app/javascript/dashboard/components/widgets/conversation/ReplyBox.vue

@@ -2,6 +2,7 @@
   <div class="reply-box" :class="replyBoxClass">
     <banner
       v-if="showSelfAssignBanner"
+      action-button-variant="link"
       color-scheme="secondary"
       :banner-message="$t('CONVERSATION.NOT_ASSIGNED_TO_YOU')"
       :has-action-button="true"