[IIS] Update aggregator function for a few fields having metric_type counter.

[ritalwar]

• Bug

What does this PR do?

This PR updates the aggregator function from average to max for few counter fields of IIS visualisations.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Related issues

• Relates [IIS] TSDB Enablement #6267

Screenshots

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Build stats

• Start Time: 2023-07-04T06:10:41.420+0000

• Duration: 14 min 26 sec

Test stats 🧪

Test	Results
Failed	0
Passed	29
Skipped	0
Total	29

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (2/2)	💚
Files	100.0% (2/2)	💚 2.909
Classes	100.0% (2/2)	💚 2.909
Methods	85.714% (30/35)	👎 -6.433
Lines	93.772% (271/289)	👍 1.913
Conditionals	100.0% (0/0)	💚

[agithomas]

LGTM!

[elasticmachine]

Package iis - 1.12.3 containing this change is available at https://epr.elastic.co/search?package=iis