Horizons SCOUT support

[dahlend]

Add support for querying the SCOUT service.
Here is a bit of code which allows for fetching the monte-carlo states from NEOCP.

    import requests
    import numpy as np
    
    def fetch_neocp_states(obj_identifier):
    
        res = requests.get(f"https://ssd-api.jpl.nasa.gov/scout.api?tdes={obj_identifier}&eph-start&orbits=true")
        res.raise_for_status()
        orbit = res.json()['orbits']
        columns = orbit['fields']
        data = [[float(x) if x != 'NULL' else np.nan for x in y] for y in orbit['data']]
        
        column_ind = {c: idx for idx, c in enumerate(columns)}
        
        lookup = {
            "desig":"idx",
            "epoch": "epoch",
            "eccentricity": "ec",
            "inclination": "inc",
            "lon_of_ascending": "om",
            "peri_arg": "w",
            "peri_dist": "qr",
            "peri_time": "tp",
        }
        lookup_rev = dict(x[::-1] for x in lookup.items())
        
        states = []
        for row in data:
            kwargs = {k: row[column_ind[v]] for k, v in lookup.items()}
            kwargs['desig'] = obj_identifier + str(int(kwargs['desig']))
            states.append(kete.CometElements(**kwargs).state)
        return states