[azure-metrics-exporter]: fix broken servicemonitor.metricprobe.yaml

[x418]

What this PR does / why we need it

This fixes the invalid condition (to check for namespaceSelector) that prevents template from rendering.

i.e. When probes exist, the template no longer renders as shown below

Error: template: azure-metrics-exporter/templates/prometheus/servicemonitor.metricprobe.yaml:23:16: executing "azure-metrics-exporter/templates/prometheus/servicemonitor.metricprobe.yaml" at <.Values.prometheus.monitor.namespaceSelector>: nil pointer evaluating interface {}.prometheus

Which issue this PR fixes

• fixes issue caused by https://github.com/webdevops/helm-charts/pull/56

Special notes for your reviewer

Checklist

• [x] Chart Version bumped
• [x] Title of the PR starts with chart name (e.g. [azure-metrics-exporter])

[ThomasMinor]

This PR also seems to fix https://github.com/webdevops/helm-charts/issues/60

[ThomasMinor]

Is there any date planned for his to get integrated?

[antonKirkPalark]

@mblaschke approve pls