Create Document Loader submodule for CCC
## Problem/motivation
Follow up to:
- #3586247+s
- #3586228+s
## Solution
Create a submodule for document loader, e.g. ai_context_document_loader.
Have it support the following in MDXEditor:
- PDF
- Text/MD
- URL (singular)
We might be able to get it set up so that we have one module and use progressive enhancement where if they add a module dependency then it just shows up.
## Tasks
- [x] Finalize approach
- [x] Update code
- [ ] Review and test
issue