Add basic document indexing and collection management UI

Basic support for indexing documents and querying them needs to be added as described on https://design.xwiki.org/xwiki/bin/view/Proposal/X-AI/WAISE/High-level%20Architecture/#HKnowledgeIndex

Basic features include:

• Chunking API and one simple chunking method, e.g., just based on a number of characters.
• Queue for indexing requests
• Queue consumer that chunks the document, embeds chunks and stores them in the vector index
• UI for managing collections