[KeyVault] Migrate or retire stand-alone samples (Azure#57907)

* [KeyVault] Migrate or retire stand-alone samples

 The focus of these chagnes is to move `getcert` and
 `keyvaultproxy` samples from `sdk/keyvault/samples/`
 to the centralized `samples/keyvault/` directory.
 The the sharelink sample is being retired as it is
 for a legacy feature that goes against Microsoft
 security guidance and has no updates planned.

 Details:
 - Move getcert and keyvaultproxy samples to samples/keyvault/
 - Retire sharelink (deprecated KV-managed storage accounts feature)
 - Delete sdk/keyvault/samples/ build infrastructure
 - Strip IsSample/IsSamplesProject conditional blocks from csproj files
 - Bump Azure.Identity, Azure.Core, KV.Certificates, KV.Secrets,
   System.CommandLine, xunit, and test SDK to latest stable versions
 - Rename getcert.csproj to GetCert.csproj for C# naming conventions
 - Update stale sample links in TROUBLESHOOTING.md, MigrationGuide.md,
   and KeyVaultCertificate.cs to point to new locations
 - Remove keyvaultproxy test entry from splittestdependencies inputs
 - Update READMEs: .NET Core 3.1 references to .NET 10

* Fixing sample links; the sample browser will publish to the existing locations, so the links are safe

Author: jsquire

eng/scripts/splittestdependencies/tests/inputs/projects.txt

@@ -84,7 +84,6 @@ $(RepoRoot)sdk\keyvault\Azure.Security.KeyVault.Administration\tests\Azure.Secur
 $(RepoRoot)sdk\keyvault\Azure.Security.KeyVault.Certificates\tests\Azure.Security.KeyVault.Certificates.Tests.csproj
 $(RepoRoot)sdk\keyvault\Azure.Security.KeyVault.Keys\tests\Azure.Security.KeyVault.Keys.Tests.csproj
 $(RepoRoot)sdk\keyvault\Azure.Security.KeyVault.Secrets\tests\Azure.Security.KeyVault.Secrets.Tests.csproj
-$(RepoRoot)sdk\keyvault\samples\keyvaultproxy\tests\AzureSamples.Security.KeyVault.Proxy.Tests.csproj
 $(RepoRoot)sdk\logic\Azure.ResourceManager.Logic\tests\Azure.ResourceManager.Logic.Tests.csproj
 $(RepoRoot)sdk\machinelearningservices\Azure.ResourceManager.MachineLearning\tests\Azure.ResourceManager.MachineLearning.Tests.csproj
 $(RepoRoot)sdk\managedserviceidentity\Azure.ResourceManager.ManagedServiceIdentities\tests\Azure.ResourceManager.ManagedServiceIdentities.Tests.csproj

samples/keyvault/getcert/GetCert.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <NoWarn>
+      $(NoWarn);
+      CA1810;
+      AZC0100;
+    </NoWarn>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Azure.Identity" Version="1.20.0" />
+    <PackageReference Include="Azure.Security.KeyVault.Certificates" Version="4.8.0" />
+    <PackageReference Include="Azure.Security.KeyVault.Secrets" Version="4.9.0" />
+    <PackageReference Include="System.CommandLine" Version="2.0.5" />
+  </ItemGroup>
+
+</Project>