Part of [#711] Similar to `Counter`, add an `UpDownCounter` instrument. Refer to the [API specs](https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/metrics/api.md#updowncounter).
Part of [#711]
Similar to
Counter, add anUpDownCounterinstrument.Refer to the API specs.