Add Support for Tracking Multi iKey Usage & Feature Statsbeat Handler

[JacksonWeber]

This pull request introduces a new StatsbeatFeaturesManager utility class for managing statsbeat features and instrumentation using bitmap flags, updates the handling of statsbeat features in the TelemetryClient class, and adds comprehensive unit tests for these changes. The most important changes include the creation of the StatsbeatFeaturesManager, updates to the TelemetryClient to track instance counts and enable the MULTI_IKEY feature, and the addition of new unit tests for both the StatsbeatFeaturesManager and TelemetryClient.

Feature Management Enhancements:

• Introduced the StatsbeatFeaturesManager utility class to manage statsbeat features and instrumentation using bitmap flags. This includes methods to enable, disable, and check the status of specific features or instrumentation. (src/shared/util/statsbeatFeaturesManager.ts, src/shared/util/statsbeatFeaturesManager.tsR1-R123)
• Added the CUSTOMER_STATSBEAT and MULTI_IKEY features to the StatsbeatFeature enum for enhanced feature tracking. (src/shim/types.ts, src/shim/types.tsR354-R355)

TelemetryClient Updates:

• Updated the TelemetryClient to track the number of instances created and enable the MULTI_IKEY feature when multiple instances are initialized. (src/shim/telemetryClient.ts, src/shim/telemetryClient.tsR53-R59)
• Integrated the StatsbeatFeaturesManager into the TelemetryClient to manage feature flags dynamically. (src/shim/telemetryClient.ts, src/shim/telemetryClient.tsL29-R37)

Unit Tests:

• Added unit tests for the StatsbeatFeaturesManager, covering initialization, feature management, instrumentation management, and error handling for malformed environment variables. (test/unitTests/shared/util/statsbeatFeaturesManager.tests.ts, test/unitTests/shared/util/statsbeatFeaturesManager.tests.tsR1-R145)
• Extended the TelemetryClient unit tests to validate instance count tracking and the enabling of the MULTI_IKEY feature when multiple instances are created. (test/unitTests/shim/telemetryClient.tests.ts, test/unitTests/shim/telemetryClient.tests.tsR367-R498)This update is intended to allow us to track multiple telemetry client usage in feature statsbeat.

[hectorhdzg]

LGTM