Metadata implementation

Metadata fields (text, date, taxonomy) are defined in Metadata Settings. Taxonomy fields automatically register a taxonomy with a doc_ prefix.

• Fields: Bcgov\Bcew\DocumentRepository\DocumentMetadataManager::get_metadata_fields
• Taxonomies: Bcgov\Bcew\DocumentRepository\DocumentPostType::register_metadata_taxonomies
• Updated action: bcgov_document_repository_metadata_fields_updated