Convert config key to map<string, String> and provide custom unmarsha…

[clun]

What This PR Does

This PR resolves a configuration mismatch when setting API feature flags via environment variables.

Previously, feature flags whose enum names contained underscores (for example, BILLING_EVENTS_LOGGING) could not be configured correctly through environment variables. This occurred because SmallRye Config automatically translates underscores (_) to dots (.), which conflicted with the existing enum-to-string conversion logic.

By changing feature flag configuration keys from enum types to strings at the configuration boundary and performing explicit conversion at runtime, both property-based and environment-variable-based configuration now work consistently.

Related Issue

Fixes #2506

Changes

1. FeaturesConfig.java

• Changed the configuration mapping from:

  Map<ApiFeature, String> flags()

  to:

  Map<String, String> flags()

• Added comprehensive JavaDoc documentation covering:

  • Configuration using property files
  • Configuration using environment variables
  • SmallRye Config's automatic underscore-to-dot translation behavior

• Added configuration examples for both approaches

2. ApiFeatures.java

• Added marshallFromConfig(Map<String, String>) to convert configuration keys to ApiFeature enums
• Added findFeatureByName(String) helper method to support kebab-case feature flag lookup
• Updated the constructor to accept Map<String, String> and perform explicit marshalling
• Added robust validation and error handling that:
  • Detects invalid feature flag names
  • Provides clear, actionable error messages
  • Lists all supported feature flag names

3. BillingTest.java

• Updated test mocks to use string-based feature flag keys (for example, "billing-events-logging") instead of enum values
• Verified configuration values take precedence over request headers
• Verified request headers can enable features when configuration is not set
• Preserved all existing test coverage

Configuration Examples

Property File (application.yaml)

stargate.feature.flags.lexical: true
stargate.feature.flags.billing-events-logging: true

Environment Variables

export STARGATE_FEATURE_FLAGS_LEXICAL=true
export STARGATE_FEATURE_FLAGS_BILLING_EVENTS_LOGGING=true

Checklist

• Changes manually tested
• Automated tests added/updated
• Documentation added/updated
• https://cla.datastax.com/

[github-actions]

📈 Unit Test Coverage Delta vs Main Branch

Metric	Value
Main Branch	52.97%
This PR	52.99%
Delta	🟢 +0.02%
✅ Coverage improved!

[github-actions]

Unit Test Coverage Report

Overall Project	52.99% -0.02%	🍏
Files changed	75.76%	🍏

File	Coverage
ApiFeatures.java	81.71% -13.71%	🍏

[github-actions]

📈 Integration Test Coverage Delta vs Main Branch (dse69-it)

Metric	Value
Main Branch	71.43%
This PR	71.43%
Delta	🟢 +0.00%
✅ Coverage improved!

[github-actions]

Integration Test Coverage Report (dse69-it)

Overall Project	71.43% -0.02%	🍏
Files changed	73.74%	🍏

File	Coverage
ApiFeatures.java	77.14% -14.86%	🍏

[github-actions]

📈 Integration Test Coverage Delta vs Main Branch (hcd-it)

Metric	Value
Main Branch	72.75%
This PR	72.75%
Delta	🟢 +0.00%
✅ Coverage improved!

[github-actions]

Integration Test Coverage Report (hcd-it)

Overall Project	72.75% -0.02%	🍏
Files changed	73.74%	🍏

File	Coverage
ApiFeatures.java	73.71% -14.86%	🍏