Update thanks for purchase banner to Pajamas::BannerComponent

What does this MR do and why?

This MR is part of Pajamas migration day. Originally I changed the banner to the new Pajamas banner, however after discussion, we decided it would be best to use an alert instead.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open `app > views > groups > show.html.haml'
2. Change lines 5 and 6:

line 5 and 6 before

- if show_thanks_for_purchase_banner?
  = render_if_exists 'shared/thanks_for_purchase_banner', plan_title: plan_title, quantity: params[:purchased_quantity].to_i

line 5 and 6 after

= render 'shared/thanks_for_purchase_banner', plan_title: plan_title, quantity: params[:purchased_quantity].to_i

3. Open up a group, e.g. gdk.test:3000/group to see the banner

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #362620 (closed) Pajamas Migration Day component:banner