Update example processes to use assets

[SariSaar]

• Update instant-booking process to use translation and branding assets
  • Add instant booking en.json file
  • Fix transaction page link in instant-booking booking-review-by-customer-wanted template
• Update automatic-off-session-payment process to use translation and branding assets
• Add missing email branding asset color to a handful of default-booking templates
  NB: Some of the email templates were updated to use existing email text keys. Those keys are not added in the en.json files to avoid duplication.