Implement discovery level search

• Added new endpoint to allow free-text searching of collections and catalogues:
  • New endpoints:
    • Discovery Search (GET/POST)
  • This queries title, description and keyword fields when available
• Added support for catalogues to split up collections and items into catalogues of data
  • This leads to updates for the following endpoints to filter by catalogues:
    • Get Collection
    • Get ItemCollection
    • Get CatalogCollections
    • Create Item
    • Update Item
    • Delete Item
    • Create Collection
    • Update Collection
    • Delete Collection
  • New endpoints added for catalogues:
    • Update Catalog
    • Create Catalog
    • Delete Catalog
    • Get Catalogs

Other changes

• Minor update to the datetime handling for Get ItemCollection to include string converter.
• Formatting changes using Black and Ruff