Add configuration and framework config to .NET hook executor

Background & Motivation
The .NET hook executor builds with an empty configuration (SDK default = Debug), while the framework service hardcodes Release. Users need control over the build configuration for hook scripts, especially for production seed/migration hooks. Multi-targeting users also need to specify a target framework moniker. Issue #7653 explicitly calls out both properties.

User Story
As a .NET developer, I want to specify configuration and framework in my hook config so that my .NET hooks build and run with the correct settings.

Solution Approach

• Define a strongly-typed dotnetHookConfig struct and unmarshal from execCtx.Config:

  type dotnetHookConfig struct {
      Configuration string `json:"configuration"` // Debug, Release, or custom
      Framework     string `json:"framework"`     // net8.0, net10.0, etc.
  }

• Read config in dotnet_executor.go Prepare() phase via execCtx.Config
• Pass Configuration to dotnetCli.Build() instead of empty string
• Pass Framework as --framework flag to dotnet run in Execute() phase
• Validate both are strings (no enum restriction for Configuration — MSBuild allows custom values like Staging)

Example azure.yaml

hooks:
  postprovision:
    run: ./hooks/migrate.cs
    kind: dotnet
    config:
      configuration: Release
      framework: net10.0

Acceptance Criteria

• config.configuration: Release builds hook script in Release mode
• config.configuration: Debug explicitly builds in Debug mode
• config.framework: net10.0 targets specific framework for both build and run
• Omitting configuration preserves current behavior (empty string → SDK default)
• Omitting framework preserves current behavior (auto-detected from project)
• Both can be specified together
• Config is unmarshalled into a strongly-typed struct (not raw map access)
• Unit tests covering configuration override, framework override, combined, and fallback

Defaults when omitted:

• configuration: empty string (SDK default, typically Debug)
• framework: not set (auto-detected from project file)

Out of Scope

• Custom dotnet run arguments — future enhancement
• Suppressing DOTNET_NOLOGO — low priority
• Runtime identifier (-r) support — future enhancement

Testing Expectations

• Unit tests: table-driven tests for config unmarshalling and dotnet CLI argument construction
• Test that configuration is passed to both Build() and Run() commands
• Test that framework is passed as --framework flag to Run() command

Related Issues

• Depends on Add generic config property bag to HookConfig #7653 / PR Add executor-specific config property bag to hooks with strongly-typed schema #7690 — provides the Config map[string]any on ExecutionContext
• Parent Epic: Multi-Language Hook Support: Python, JavaScript, TypeScript, .NET #7435 — Multi-Language Hook Support