Make an `autocontract` directive

[antazoey]

Overview

I want to be able to use auto-doc like directives for contracts so projects like ApePay can have docs for generated for the contracts.
Really, any Ape-project will be doc-able this way, and would make sense to make an ape-docs plugin at that point.

Specification

Exceptions

```{eval-rst}
.. autocontract:: StreamManager
    :members:

### Dependencies

Include links to any open issues that must be resolved before this feature can be implemented.

[linear]

APE-1809 Make an `autocontract` directive