Support to MetricNamespace

[raphaelquati]

Support MetricNamespace field to query CustomMetrics (like Telegraf metrics)

Docs: https://docs.microsoft.com/en-us/rest/api/monitor/metricnamespaces/list https://docs.microsoft.com/en-us/rest/api/monitor/metricdefinitions/list https://docs.microsoft.com/en-us/rest/api/monitor/metrics/list

[dylan-asos]

+1 yes please!

[nhjiejan]

+1. Need this for Guest OS metrics, would be tremendously useful