Add unit tests for Global Settings module and related types

- Implement tests for GlobalSettingsInitService covering methods like getAllSettings, getSettingsByGroup, loadSettingsDefinitions, and configuration getters.
- Create tests for settings modules including SMTP, GitHub OAuth, and Global settings to validate structure, required settings, and descriptions.
- Introduce type validation tests for GlobalSettingType, GlobalSettingDefinition, GlobalSettingGroup, GlobalSettingsModule, SmtpConfig, GitHubOAuthConfig, GlobalConfig, ValidationResult, and InitializationResult.
- Ensure cross-module validation for unique group IDs and setting keys, consistent sort order, and appropriate default values.

Author: Lasim

.gitignore

@@ -56,9 +56,14 @@ fastly-events.log
 deploystack.db
 services/backend/persistent_data/*
 
+# Test files
+services/backend/tests/.test-context.json
+services/backend/tests/e2e/test-data/*.db
+
 ._*.ts
 ._*.vue
 ._*.md
 ._*.js
 ._*.json
 cookies.txt
+cookiejar.txt