add new clients to namespace counts

[miagilepner]

Description

I realized I missed something when reviewing the original PR - this needs to be adding the new counts to the existing precomputed query, not the total counts. My bad!!

Updated the test to verify that we're combining the NewClients.Namespaces field, and not Namespaces.

TODO only if you're a HashiCorp employee

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[divyaac]

Thanks for catching this!! Approved, just pending tests

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CI Results:
All Go tests succeeded! ✅

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Build Results:
All builds succeeded! ✅