Add error/warning logging to shape matcher and rewrite README
- Inject LoggerChannelFactoryInterface into EntityReferenceShapeMatcher
- Log error in resolveFieldKey() when entity type definition cannot be loaded, so administrators can identify misconfigured props in the logs
- Log warning in resolveEntityTypeId() when an array items $ref URI is set but not recognised, pointing to the fix
- Rewrite README.md to cover all current annotations: x-entity-type, x-entity-field, x-entity-type-bundles, x-entity-widget, entity_render() multi-entity-type support, updated configuration and troubleshooting