Add environment variable to disable feature management schema compatibility logic

[amerjusupovic]

This PR adds the environment variable AZURE_APP_CONFIGURATION_FM_SCHEMA_COMPATIBILITY_DISABLED. When set to true, the provider will process and output all feature flags as the newer Microsoft schema. If false, the provider will function as it does today where a flag is only processed in the Microsoft schema if any of the variants, allocation, or telemetry properties are present.

[Copilot]

Pull Request Overview

This PR introduces an environment variable to disable schema compatibility logic in the feature management provider, forcing all feature flags to use the Microsoft schema when enabled.

• Add AZURE_APP_CONFIGURATION_FM_SCHEMA_COMPATIBILITY_DISABLED support in FeatureManagementKeyValueAdapter
• Update conditional logic to respect the new environment variable
• Add a new unit test covering forced Microsoft schema behavior

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Microsoft.Extensions.Configuration.AzureAppConfiguration/FeatureManagement/FeatureManagementKeyValueAdapter.cs	Read the new environment variable and adjust schema selection logic
tests/Tests.AzureAppConfiguration/Unit/FeatureManagementTests.cs	Add test verifying behavior when the environment variable is set or unset

Comments suppressed due to low confidence (2)

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/FeatureManagement/FeatureManagementKeyValueAdapter.cs:22

• [nitpick] Consider renaming this constant to DisableFmSchemaCompatibilityEnvironmentVariableName to clearly indicate it holds the environment variable name.

        private const string DisableFmSchemaCompatibilityEnvironmentVariable = "AZURE_APP_CONFIGURATION_FM_SCHEMA_COMPATIBILITY_DISABLED";

tests/Tests.AzureAppConfiguration/Unit/FeatureManagementTests.cs:2345

• Add a unit test for explicitly setting the environment variable to an invalid value (e.g., "notabool") to verify the default behavior fallback.

            // Act - Verify normal behavior when environment variable is not set