Implement email notification with the order details

[sorokinvj]

We are going to use Sendgrid as our email provider.

Here is what we need to do:

• register an account on Sendgrid (Vlad)
• Create an email template that is mobile-friendly and tested with the most popular email clients/services:
  - ios native mail
  - gmail
  - outlook
• when we have tested HTML, we are going to create a template on Sendgrid and then integrate Sendgrid with our app. Probably the best place to send email is pages/api/stripe/webhook.ts

          case 'checkout.session.completed':
            await createOrder({ sessionId: event?.data?.object?.id })
            await sendEmail({id: ORDER_SUCCESSFUL}) // or something along this line
            break