Add Richt Text Editor to Create/Edit Email Contents

[airelawaleria]

Right now PROMPT is relying on hard-coded email contents that is beeing sent out to students e.g. upon successful application form submission or interview invites.

AC:

• There is a separate section in the management console to review and edit the email contents
• The contents are editable and are stored as markdown (https://mantine.dev/others/tiptap/)