fix: replaced deprecated MongoDB count() with countDocuments

[neturmel]

Pull Request Template

Summary

MongoDB count() function was deprecated, so it must be replaced with countDocuments()

Change Type

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• [X ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Translation update

Testing

It is only a change of a function name

Test Configuration:

Checklist

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• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• My changes do not introduce new warnings
• Local unit tests pass with my changes

[yanglicb]

Also found it and thought the same, thank you!

[wipash]

If you need a short term workaround in a running container:

sed -i 's/\.count(/\.countDocuments(/g' config/user-stats.js

[danny-avila]

thanks, cherry-picked this commit in #4951