Users can change their newsletter subscription status in the settings
view.

Empty branch IDs and missing payment information caused network errors
and a missing billing component.

Includes the associated Go functions for inserting and selecting given a
specific user ID or subscription ID. Also adds required HTML tags and
HTTP queries for subscription process during user registration.

To make requests to Go API endpoints for registration from a PHP page,
there needs to be local routing between the two servers. This method
avoids needing Apache installed seperately for development builds while
allowing it to still be used in production if necessary.

Secures the user registration endpoint.

A new template file needed to be created to allow custom javascript in
a grav page. The JS file will mount the transpiled Vue app.