Separate admin and API URLs

[lukebennett]

This is borderline feature vs bug.

At the moment there is a single URL that can be set in config, serverURL, which is then appended to with either the admin or API routes via the getAdminURL or getAPIURL helper methods.

I've seen it stated elsewhere that it's fine to host the admin portal and the API separately, however the above limitation leads to issues doing this.

For example, when first splitting my environment out (https://admin.xxx.com and https://api.xxx.com), I saw certain API requests within the admin portal fail when serverURL was set to the admin URL, I had to change it to the API URL for it to work. However, this means that any reference to getAdminURL() is now incorrect as it references the same config option.

We could therefore do with a second config option for the API that could default to serverURL when not set, and then make sure that this is used as appropriate across the app. There are probably also other ways it could be made easier to split the two environments out, such as improved docs.