Simplify the IPAC/IRSA MOST Service interface.

As discussed in https://github.com/astropy/astroquery/pull/2660#discussion_r1230361245 the interface to MOST service is kind of complicated. In https://github.com/astropy/astroquery/pull/2660 the implementation presents a mirror-like interface to the online interface. However this duplicates some data, and needlessly complicates interpretation of the results in Python.

The interface would be significantly improved if the returned results would be simplified by always returning
* the ephemerides
* a joined metadata table constructed by merging and de-duplicating the `Results Table` and `Image Metadata with a Matched Object Position`
* the query parameters values, for query parameters that have a list of values, were made to be case-insensitive on astroquery side

Start with the MOST service implementation and the discussion in pull request #2660. Trace how its current results mirror the online interface, then compare that behavior with the requested ephemerides, joined de-duplicated metadata, and case-insensitive list-valued query parameters. Done means the simplified interface is implemented and its behavior is covered by the relevant existing checks.

Written by the indexing model from the issue text.