Make metric temporality configurable

[pol-colomo]

The default temporality of the metrics are in delta and would be good to have this configurable through env or yaml config to be able to switch to cumulative instead.

This would be very useful for integrations with Graphana for example, that expects metrics as cumulative.

const OTLPExporter = new OTLPMetricExporter({
    url: 'otlpendpoint.com',
    temporalityPreference: AggregationTemporality.CUMULATIVE // env variable
})