Rename `dns.lookupS.duration` to `dns.lookup.duration`

[antonfirsov]

The name implemented in #89813 is result of a misunderstanding. https://github.com/lmolkova/semantic-conventions/blob/dotnet8-metrics/docs/dotnet/dotnet-dns-metrics.md#metric-dnslookupsduration has a typo in the title, but lower in the table it's correctly spelled as dns.lookup.duration which is a name that aligns with OTel conventions.

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Issue Details

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The name implemented in #89813 is result of a misunderstanding. https://github.com/lmolkova/semantic-conventions/blob/dotnet8-metrics/docs/dotnet/dotnet-dns-metrics.md#metric-dnslookupsduration has a typo in the title, but lower in the table it's correctly spelled as dns.lookup.duration which is a name that aligns with OTel conventions.

Author:	antonfirsov
Assignees:	-
Labels:	area-System.Net
Milestone:	8.0.0

[antonfirsov]

Fixed by #93414 in release/8.0, and by #93254 in main (9.0).