[AI Bundle][Store] Add FilterInterface and filters support to Indexer

[OskarStark]

Q	A
Bug fix?	no
New feature?	yes
Docs?	yes
Issues	--
License	MIT

• Add FilterInterface similar to TransformerInterface
• Implement TextContainsFilter for content-based filtering
• Integrate filters into Indexer pipeline (load → filter → transform → vectorize)
• Add filters configuration to AI Bundle
• Update demo configuration with Week of Symfony filter
• Add comprehensive test coverage for filter functionality
• Include example in examples/indexer/index-with-filters.php

Filters run after document loading but before transformers, allowing removal of unwanted content before vectorization and storage.