Follow semantic conventions for naming graphql spans

The current graphql instrumentation does not follow span naming conventions detailed here. The documentation states the following: The span name MUST be of the format <graphql.operation.type> <graphql.operation.name> provided that graphql.operation.type and graphql.operation.name are available. If graphql.operation.name is not available, the span SHOULD be named <graphql.operation.type>. When <graphql.operation.type> is not available, GraphQL Operation MAY be used as span name.

The relevant code looks to be here, where graphql.operation.type and graphql.operation.name are added as span attributes but the span is then named graphql.execute_query.

This change would also align with other libraries that already follow this convention, such as nodejs's instrumentation for graphql seen here.