Add ExportProps when exporting emails

[badalya1]

Goals

1. Provide a way to set props for exporting
2. Used when uploading generated templates to service providers

Background

When running email dev, the UI renders the emails with the PreviewProps. When exporting though all those values are unavailable.

Proposal

We should make a way to export templates to align compatibility with service providers.

Example.

VercelInviteUserEmail.ExportProps = {
  username: '{{user.name}}',
  userImage: '{{user.image}}',
  invitedByUsername: '{{user.invitedBy}}',
  invitedByEmail: '{{user.invitedByEmail}}',
  teamName: '{{team.name}}',
  teamImage: '{{team.image}}',
  inviteLink: '{{inviteLink}}',
  inviteFromIp: '{{inviteIp}}',
  inviteFromLocation: '{{invaiteLocation}}',
} as VercelInviteUserEmailProps;

Now when running email export, these props will be used to export temaplates ready to be uploaded to a service provider. e.g Sendgrid