Use GlAvatar in `app/assets/javascripts/frequent_items/components/frequent_items_list_item.vue`

We're rendering some avatars in this component that don't use GlAvatar.

This should be refactored to use GlAvatar.

Existing Avatar code

      <div
        ref="frequentItemsItemAvatarContainer"
        class="frequent-items-item-avatar-container avatar-container rect-avatar s32"
      >
        <img v-if="avatarUrl" ref="frequentItemsItemAvatar" :src="avatarUrl" class="avatar s32" />
        <identicon
          v-else
          :entity-id="itemId"
          :entity-name="itemName"
          size-class="s32"
          class="rect-avatar"
        />
      </div>