feat(inputs.sqlserver): Get Database Pages performance counter

[goswamisandeep]

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resolves #

[goswamisandeep]

As per the blog https://learn.microsoft.com/en-us/sql/relational-databases/performance-monitor/monitor-memory-usage?view=sql-server-ver16

SQL Server: Buffer Manager: Database Pages

This counter indicates the number of pages in the buffer pool with database content. Does not include other nonbuffer pool memory within the SQL Server process. Query this counter using the sys.dm_os_performance_counters dynamic management view.

[telegraf-tiger]

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[srebhan]

Looks good from my side, but I again want to hear @Trovalo's opinion.

[Trovalo]

I've nothing against it but I honestly don't see it as a useful counter. If the aim is to check if the server is under memory pressure it's better to check the Page Life Expectancy.