22399 create published files for plates and nuke script

Creates published file entities for nuke script and plate renders. Adds Metadata nodes for each entry in the tk-nuke-writenode app settings for the context (requires code from https://github.com/shotgunsoftware/tk-nuke-writenode/pull/1)

Note: json is only used to help with stringifying dict data

We had discussed adding a setting for the default name for the exported nuke script but I just realized I didn't add that. Let me know if you think it should get in. If so, what happens to the setting the user creates in the export dialog? Or do we create another token, something like `{tk_nukescript_filename}`? Easy to add if we should do it.