docs: add node api migration docs

[psychedelicious]

What type of PR is this? (check all applicable)

• Documentation Update

Description

• Update mkdocs config
• Add mkdocstrings to auto-document invocation context
• Fix some invocation context arg names (sorry, this should be in a separate PR but I wanted to test the docs generation together)
• Add docs for v3 -> v4 migration and the public API

QA Instructions, Screenshots, Recordings

• pip install -e ".[docs]" to get latest deps, you may need to add --force-reinstall` to get updated versions
• mkdocs serve to generate and browse the new docs - they are under Workflows & Nodes

Merge Plan

This PR can be merged when approved

[optional] Are there any post deployment tasks we need to perform?

Ensure that the docs page updates - we may need to manually kick that off once next merges to main.