Add examples to dotnet-gcdump doc

[Youssef1313]

Following the pattern of https://raw.githubusercontent.com/dotnet/docs/master/docs/core/diagnostics/dotnet-counters.md we should have an Examples h3 section following each Options h3 section.

Originally posted by @tdykstra in https://github.com/dotnet/docs/pull/19697

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Document Details

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• ID: 0aa2e42f-838c-92e9-1125-7540721952e6
• Version Independent ID: 665bb8b1-6024-24d1-46df-8ae4789fe1a1
• Content: dotnet-gcdump diagnostic tool - .NET CLI
• Content Source: docs/core/diagnostics/dotnet-gcdump.md
• Product: dotnet-fundamentals
• GitHub Login: @sywhang
• Microsoft Alias: suwhang

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Associated WorkItem - 537141