Clean up interpolation of time dimensions in various sub-xdss

[FedeMPouzols]

We have very similar code doing the same thing to interpolate and rename time_pointing, time_ephemeris, time_syscal, time_phase_cal to the main_xds time, after last few rounds of updates to the schema.

• Clean this up and unify into single function(s).
• While looking into this I also realized that when not interpolating pointing, its time dimension was not named correctly. Fix that.