Add support for stubs in InferencePipeline

[PawelPeczek-Roboflow]

Description

In this PR we make it possible for InferencePipeline to work with stubs (model/0) and with Roboflow models other than object-detection ones. We adjusted sinks to work with other type of output.

List any dependencies that are required for this change.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How has this change been tested, please provide a testcase or example of how you tested the change?

• maintained regression
• run the changes locally to verify

Any specific deployment considerations

For example, documentation changes, usability, usage/costs, secrets, etc.

Docs

• Docs updated? Partially (at the docstring level) - @capjamesg if u could post something in high-level docs that would be great.