[FR] `INCLUDE_PATTERN` for `apidoc`

[abravalheri]

Is your feature request related to a problem? Please describe.
Currently you can pass EXCLUDE_PATTERN to sphinx-apidoc and that is very good to prevent documentation to be generated for modules that are not intended. This is nice when the majority of the modules is intended for public consumption but there are a few exceptions.

However it can be very frustrating when the code-base works on the other way around: the majority of the modules are not intended for public consumption but there are a few that should be documented.

For example, consider a package where all the modules intended for public consumption are names *_api.py and the author wants sphinx-apidoc to only generate documentation for them.

Describe the solution you'd like
Add a INCLUDE_PATTERN argument/option to sphinx-apidoc

Describe alternatives you've considered
I tried to mess around a bit with autogen, but it does not have the same functionality as the suggestion.