pydeephaven should have the ability to fetch InputTable instances

[niloc132]

As a developer, working in an environment where there is a shared InputTable on the server in the global scope, I would like the ability to not only open that table and read its contents, but write to it as well.

Options for this could include adding another parameter to session.open_table to specify the type of table to fetch, or a new method to access input tables.

We already have the ability to create and to manipulate input tables from python clients, this feature request is limited to accessing existing input tables.