FEAT allow for easier querying for supported input / output types in converters

[romanlutz]

Is your feature request related to a problem? Please describe.

Currently, you can get the supported input types by iterating through all types (like text below) and running it through

converter.input_supported("text")

But you'd need to know all the types. That also only gets you input types, not output types.

Describe the solution you'd like

This may be preferable:

coverter.supported_input_types
["text", "audio"]

We could do the same for output types, of course.