Return a fully-qualified document_path string.

def document_path_path(cls, project, database, document_path):
        """Return a fully-qualified document_path string."""
        return google.api_core.path_template.expand(
            "projects/{project}/databases/{database}/documents/{document_path=**}",
            project=project,
            database=database,
            document_path=document_path,
        )