Rename NB_API_QUERY_URL to NB_API_URL or similar

[alyssadai]

NB_API_QUERY_URL can be slightly confusing because it:

1. Does not refer to the query tool URL
2. Does not refer only to the /query endpoint for the API, rather it is the base URL for the API which endpoints are appended to

To improve clarity and prevent confusion with NB_QUERY_APP_BASE_PATH, maybe we can consider renaming this to simply NB_API_URL or NB_FAPI_URL.