Implement velocity aberration

[schlafly]

romanisim is currently ignoring the aberration of starlight. We should put this into the simulations and into the pipeline processing.

Some notes on how this should be implemented are available here:
spacetelescope/romancal#1192

We would just build this in as an additional term in the gWCS, as we would in romancal. We should check to see if the GalSim implementation includes aberration or not.

We would also need to put in the ephemerides. There should be something simple to assume on the order of the spacecraft always being exactly at L2, so its velocity is the same as the Earth's, times roughly 1.01.