fix: set interval (granularity) in Azure Monitor API request

[nicknikolakakis]

Fixes #7524

Summary

The azure-monitor scaler was not setting the Interval (granularity) parameter when querying the Azure Monitor metrics API. Without it, Azure defaults to PT1M granularity, returning multiple data points within the timespan. Since verifyAggregationTypeIsSupported only reads data[len(data)-1] (the last data point), the Total aggregation over a 15-minute window would only return the last 1-minute bucket's value instead of the sum over the full window.

Changes

• formatTimeSpan now also returns an ISO 8601 duration string (e.g., PT15M) matching the timespan, and requestMetric passes it as opts.Interval
• When no metricAggregationInterval is configured, both timespan and interval default to 5 minutes (PT5M)
• Added unit tests for toISO8601Duration and formatTimeSpan
• Updated CHANGELOG.md

How it works

Before	After
Interval: nil → Azure returns multiple 1-min buckets	Interval: "PT15M" → Azure returns a single data point
Only last bucket's value is used	Single aggregated value covers the full window

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