PMM-9870 fix collstats indexSizes metrics.

[BupycHuk]

PMM-9870 (optional, if ticket reported)

• Links to related pull requests (optional).
  fixes is it possible get the storageStats.wiredTiger and storageStats.indexDetails from $collStats #897
  fixes Better usability for mongodb_collstats_storageStats_indexSizes_.* metrics #882

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