Update code for realm and API host assumptions

[xgp]

Realm:

• Path realm is always the same as auth realm (keycloak.json)

API host:

• Default is that the API host is the auth host (from keycloak.json).
• We should update everywhere in the code (api clients, feature flag fetchers, etc.) where we use the API host to pull from a utility that creates the API host for them. We'll also need variants (E.g. apiHost=app.phasetwo.io, apiBaseUrl=https://app.phasetwo.io)
• We need a way to override the API host for local development by setting an environment variable. This should only be in one place, so that the code is not polluted with env.authurl | blah