Document .runtimeconfig.dev.json configProperties precedence change in .NET 11

[Copilot]

This PR documents a .NET 11 Preview 6 behavioral change: when the same configProperties key exists in both .runtimeconfig.json and .runtimeconfig.dev.json, the .runtimeconfig.dev.json value now takes precedence.

• New breaking-change article (Deployment / .NET 11)

  • Added docs/core/compatibility/deployment/11/runtimeconfigdev-configproperties-precedence.md.
  • Captures previous behavior, new behavior, reason for change, recommended action, and affected APIs (None).

• Compatibility navigation updates

  • Added the new article under Deployment in docs/core/compatibility/11.md.
  • Added the matching TOC node in docs/core/compatibility/toc.yml under .NET 11 > Deployment.

• Related runtime-config guidance update

  • Updated docs/core/runtime-config/index.md to explicitly note the new precedence rule and link to the breaking-change article.

// app.runtimeconfig.json
{
  "runtimeOptions": {
    "configProperties": {
      "System.GC.Concurrent": true
    }
  }
}

// app.runtimeconfig.dev.json
{
  "runtimeOptions": {
    "configProperties": {
      "System.GC.Concurrent": false
    }
  }
}

With .NET 11 Preview 6+, the effective value is false from .runtimeconfig.dev.json.