add fields for ssSources relevant to Roman

[joemasiero]

Current alert schema for solar system object potential associations:

rapid/alerts/schema/01/00/rapid.v01_00.ssSource.avsc

Lines 8 to 16 in 86940c7

	{"name": "ssSourceId", "type": "long", "doc": "Unique identifier for this solar system source"},
	{"name": "diaSourceId", "type": "long", "doc": "Associated diaSource identifier"},
	{"name": "ssObjectId", "type": ["null", "long"], "default": null, "doc": "Associated solar system object identifier"},
	{"name": "heliocentricX", "type": ["null", "double"], "default": null, "doc": "Heliocentric x position [AU]"},
	{"name": "heliocentricY", "type": ["null", "double"], "default": null, "doc": "Heliocentric y position [AU]"},
	{"name": "heliocentricZ", "type": ["null", "double"], "default": null, "doc": "Heliocentric z position [AU]"},
	{"name": "phaseAngle", "type": ["null", "float"], "default": null, "doc": "Phase angle [deg]"},
	{"name": "heliocentricDist", "type": ["null", "float"],"default": null, "doc": "Heliocentric distance [AU]"},
	{"name": "topocentricDist", "type": ["null", "float"], "default": null, "doc": "Topocentric distance [AU]"}

ToDo:
-Clarify that this represents the closest known solar system object
-add a fields "size of source-prediction offset" and "angle of source-prediction offset"
-add UTC_start and UTC_end times for the image
-add field "predicted V magnitude"
-change "heliocentric?" to "sun_to_object_?" based on predictions, in equatorial AU
-add fields "earth_to_sc_?" fields for X,Y,Z in equatorial KM, as well as "earth_to_sc_V?" in km/s
-clarify the coordinate systems above in documentation