DHC: Workspace dependencies

[bmingles]

We want users to have a local DH workspace experience that feels familiar to other local python dev experiences. Part of this is being able to import modules from their workspace into other workspace modules.

• Auto configuration of PYTHONPATH and / or any other defaults to allow workspace to behave as close to local python experience as possible. For DHE, this has some challenges for supporting python imports for other files in the workspace. Charles pointed me to #deephaven_enterprise.notebook.meta_import for how we do virtual python imports
• Once a dependency module is imported, it won't get updated if changes are made to the dependency. Want to figure out a way to auto update these, or an explicit refresh preferably without a full server restart

Note that for servers not managed by the extension, we may not have direct access to the file paths from the extension. This will require users to manually configure PYTHONPATH, or we could possibly employ import hooks as a means to provide modules to the server from the vscode workspace

Links on python import management:

• https://docs.python.org/3/library/importlib.html#importlib.reload
• https://docs.python.org/3/library/importlib.html#importlib.invalidate_caches
• https://docs.python.org/3/library/importlib.html#importlib.abc.MetaPathFinder.find_spec

Links on import hooks:

• https://stackoverflow.com/questions/43571737/how-to-implement-an-import-hook-that-can-modify-the-source-code-on-the-fly-using
• https://pypi.org/project/importhook/