Add constants used in LDC pipeline

• VELOCITYOFLIGHT_CONSTANT_VACUUM = 299792458.0 # [m s^-1]
• ASTRONOMICALUNIT_METER = 149597870700.0 # [m]
• SIDEREALYEAR_J2000DAY = 365.256363004 # [day]
• SUN_GM = 1.3271244210789466e+20 # [m^3 s^-2]
• PARSEC_METER = 3.0856775814913674e+16 # [m]
• NEWTON_CONSTANT = 6.674080e-11 # [m^3 kg^-1 s^-2]
• SUN_MASS = 1.98848e+30 # [kg]