Accept astropy Table as upload_resource for TAP

This is a feature request for TAP/Gaia. I think it is useful to be able to use astropy Table instance directly as `upload_resource` argument without the need to output the file to disk. Currently, it seems that the `upload_resource` argument specifically should be the filename of the file containing the table in VOTable format. I think such a feature is very useful for on-the-fly/interactive exploration.

Start by tracing the TAP/Gaia handling of the upload_resource argument and how it currently accepts VOTable filenames. Determine how an astropy Table could be accepted without writing a file, then verify that interactive uploads work while existing filename-based uploads remain supported.

Written by the indexing model from the issue text.