Dynamic API Base Url

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### Current Behavior:
Currently the frontend container requires an API_BASE_URL environment variable to populate the static/config.json, which hard couples the frontend to a domain URL.

### Proposed Behavior:
Since the frontend and apiserver can be deployed on the same domain, it would be nice if the frontend could dynamically just make a request to the domain it's hosted from. This alleviates potential CORS issues when hosted on the same domain, as browsers will default deny all other domains making requests to it.

A pattern for this i've used before, is if a base url isn't configured, fallback to using `document.location` to build the base URL.