Add `origin_mismatch` option to constraints on angular separations

As noted in the astropy document, a warning is emitted if the coordinate transformation can cause the angular separation value to be order-dependent.

https://docs.astropy.org/en/stable/coordinates/common_errors.html#object-separation

This warning can be very long when supplying a time or a target array with many elements. I'd like to have the `origin_mismatch` option with `warn` as the default for these constraints class related to object separations.

Apparently, only sun and moon constraints needs to be updated, so changes will be small. However, I'm not sure which place is the best location to do this. For example, one can set at the initialization of the class object or at `compute_constraint()` for each actrual calculation.

Start with the Sun and Moon constraint implementations and their compute_constraint() methods, then read the linked Astropy object-separation warning. Determine where the origin_mismatch option should be accepted and passed for these constraints; done means both constraints support warn by default without producing unnecessarily long warnings for time or target arrays.

Written by the indexing model from the issue text.