Update Steeltoe to build and run tests against .NET 9 RC2

[bart-vmware]

Description

Experimental and hacky, do not merge.

Open issues:

• BLOCKING: breaking changes in AggregationManager (Steeltoe copy from .NET runtime is outdated and incompatible)
• BLOCKING: Compatible MySQL drivers from Pomelo and Oracle aren't available yet
• BLOCKING: Fix S4056 AD0001: .NET 9 RC1 SonarSource/sonar-dotnet#9670 (still unresolved despite closed issue)
• BLOCKING: Added documentation on JsonSerializerOptions produces different ConfigurationSchema.json in Steeltoe.Management.Endpoint for .NET 8/9 (this becomes problematic when multi-targeting, causing build failure)
• Aspire Config schema generator is incompatible with .NET 9, due to breaking change in System.Text.Json
• Obsolete warnings (SYSLIB0057) for reading X509Certificate2 files
  • Related conversation at Dashboard should use X509CertificateLoader instead of obsolete X509Certificate2 constructor dotnet/aspire#5461
• Bug (false positive) in IDE0052 analyzer Regression in .NET 9 RC2: IDE0052 reports false positive with source-generated method  dotnet/roslyn#75483

[bart-vmware]

/azp run Steeltoe.All

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud