upsert and get are not implemented

[juongithub]

The upsert and get commands are not implemented, they might be useful.
The upsert command is similar to save:

public function upsert( $document ) {
  $document = (object) $document;
  $partitionValue = $this->findPartitionValue( $document );
  $document = json_encode( $document );
  
  $headers = $this->triggersAsHeaders( "create" );
  
  $headers['x-ms-documentdb-is-upsert'] = 'True';
  
  $result = $this->collection->createDocument( $document, $partitionValue, $headers );
  
  $resultObj = json_decode( $result );
  
  if ( isset( $resultObj->code ) && isset( $resultObj->message ) ) {
	  throw new Exception( "$resultObj->code : $resultObj->message" );
  }
  
  return $resultObj->_rid ?? null;
}

While the get should simply take advantage of the CosmoDB getDocument method already implemented.