Add findFiles and findFile graphql queries

[WithoutPants]

Adds findFiles and findFile queries to the graphql schema. Adds parent_folder and zip_file fields to the file and folder types and deprecates parent_folder_id and zip_file_id.

This can be used to create a file system view, or for plugins to better manipulate files.

Related design: https://discourse.stashapp.cc/t/design-add-support-for-querying-files/577