SampleRate should not be applied for metrics telemetry

[OsvaldoRosado]

In https://github.com/Microsoft/ApplicationInsights-node.js/blob/develop/Library/EnvelopeFactory.ts#L85
we apply the configured sample rate to all telemetry items.

In https://github.com/Microsoft/ApplicationInsights-node.js/blob/develop/TelemetryProcessors/SamplingTelemetryProcessor.ts#L13
we refuse to sample out data for metrics, but we don't reset the sample rate to 1.

We should either never apply the configured sample rate to metrics items, or reset it in the SamplingTelemetryProcessor. Never setting the configured sample rate within EnvelopeFactory sounds cleanest, as it doesn't override actions users might take themselves in their own telemetry processors.