Prettify Email Template

[klondikemarlen]

Relates to:

• Build Dataset Access Subscriptions Email Users Button #41

Context

Is your feature request related to a problem? Please describe.
Currently email template is non-existent, and content is injected as plain text in a <pre> block.
This makes all emails fairly ugly.

Describe the solution you'd like
Add markdown support to email content entry.
Add base template such as https://github.com/ytgov/pmap-survey/blob/main/src/api/src/templates/base.html
Add MJML to email base template.
Add EJS or Pug for rendering complex content.

Additional context

Current maximum email pretification using <pre> tag.