Add access to MPC checker

https://www.minorplanetcenter.net/cgi-bin/checkmp.cgi

what do you think @mommermi? I'm at a hackweek atm where having this functionality in astroquery would be so powerful

Start by reviewing the MPC checker at https://www.minorplanetcenter.net/cgi-bin/checkmp.cgi and the repository's existing patterns for accessing online data resources. Determine the requested functionality, inputs, outputs, and integration scope before proposing an implementation. Done means astroquery provides a tested way to access the MPC checker.

Written by the indexing model from the issue text.