Get an email template
Returns the template for one language: what customers receive now,
Spree’s default, and the draft with its lock_version. When Spree’s
default changed since the store’s version started from it,
default_changed is true and base_body holds the default it
started from, to compare with default_body.
Required scope: read_email_templates (for API-key authentication).
Authorizations
Secret API key for admin access
JWT token for admin user authentication
Headers
Bearer token for admin authentication
Path Parameters
The template key with dots, e.g. spree.order_mailer.confirm_email
Query Parameters
A language code, or any (the default)
Comma-separated associations to expand (draft.updated_by)
Response
email template found
email, layout, partial 
