Update to .NET Aspire preview 6

[tjementum]

Summary & Motivation

Upgrade to Aspire preview 6, a minor update that is likely the last preview before its general availability (GA). This update introduces no breaking changes.

The prerequisites in the PlatformPlatform CLI have been upgraded to check for preview 6.

Upgrade all NuGet packages to latest version including OpenTelemetry, XUnit, and FluentValidation.

Update WebAppMiddleware to await generation of index.html, fixing race condition where frontend recreates file during .NET process startup.

Checklist

• [x] I have added a Label to the pull-request
• [x] I have added tests, and done manual regression tests
• [x] I have updated the documentation, if necessary

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
21.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud