Consider optional cosmology-based distances for higher-redshift galaxies

[ceibensteiner]

Currently, galaxy distances used in distance_key.txt and related products such as moment_key.txt are treated as fixed/adopted distances. This is appropriate for nearby galaxies. However, for more distant galaxies, e.g. systems beyond roughly z 0.01–0.02, it may be useful to optionally compute distances from redshift using an adopted cosmology. This would allow more consistent handling of luminosity distances, angular-diameter distances, and physical scales for galaxies where cosmological effects are no longer completely negligible.

Suggested implementation
Consider adding an optional cosmology-based distance mode for galaxies with available redshifts.
For example:

• keep the current adopted-distance behavior as the default;
• optionally compute distances from redshift using an adopted cosmology, e.g. astropy.cosmology;
• record whether the distance is adopted;
• store/use the appropriate distance type: luminosity distance, D_L, for luminosities and flux-to-luminosity conversions; angular-diameter distance, D_A, for physical scales; possibly comoving distance only where explicitly needed.

Possible additions to distance_key.txt
Add optional columns such as:

redshift
distance_method
cosmology_name
H0
Om0
D_L_Mpc
D_A_Mpc
kpc_per_arcsec

Possible additions to moment_key.txt
If moment products depend on distance-based quantities, include enough metadata to clarify which distance was used, for example:

distance_used_Mpc
distance_type
distance_method
kpc_per_arcsec