Index configured fields only, simplify OpenSearch mapping

[pteich]

This PR adds the following changes:

• Moves SearchIndex ownership to the provider workspace. APIBinding reconciliation now creates/updates SearchIndex resources there, while indexing keeps a legacy root:orgs fallback for existing indexes.
• Simplified mapping is used to prevent maintaining large mappings in code
• Updates mapping generation so semantic fields live under semantic_fields, filterable fields use keyword dynamic templates, and field paths are normalized/deduplicated.
• The naming of index fields is adapted to be aligned with RFC
• Simplifies indexed OpenSearch documents by removing full raw/text payload indexing and replacing it with configured default_fields, semantic_fields, and filterable_fields

Refers to platform-mesh/platform-mesh#95 and platform-mesh/platform-mesh#94