Set PYTHONPATH environment variable for Python script scrapers

[Maista6969]

With the introduction of the new scraper and plugin management system in #4242 we've seen several scrapers failing because of their dependency on other packages such as py_common. Since the new management system puts these scrapers in separate folders they need to hack around this by manually adding their parent to their sys.path

To solve this in Stash itself we can set the PYTHONPATH environment variable when running Python scrapers to add the base scraper directory to the list of paths where Python will search for module imports

Notes:

• I know the variable names aren't great, but my imagination is lacking and they're entirely local.
• I would have loved to have had access to the local path configured for this scraper source, but I do not know the code base well enough to include it. Currently the scraper knows its absolute path so I simply used that to get the parent of its parent folder, but this will fail if scrapers have nested folder structures 🤷‍♂️
• I'm not familiar with any plugins that will need this so I have only added this to the scraper package