Add support for local files in custom pipelines

[vvvm23]

Is your feature request related to a problem? Please describe.
Currently there is no way to pass a local pipeline file to DiffusionPipeline as a custom pipeline. This makes the development process when adding custom pipelines quite difficult, as it requires pushing to main first or clearing the cache (see this comment)

Describe the solution you'd like
When a local path is specified, a custom pipeline should be loaded using the local file.

Describe alternatives you've considered
There are workarounds as specified in the above link. Personally, I also just added a __main__ block to the custom pipeline file and executed it directly - but this is less than ideal.

Thanks 🤗

[patrickvonplaten]

Yes very much agree! I'll try to tackle it this week - in case anybody is interested I'm more than happy to help someone guide to merge a PR here.

[patrickvonplaten]

This PR should fix it :-)
#1327

[vvvm23]

Nice, I'll close once merged :)))