Enable support for reusing plugins in multiple instances of AppInsights

[MSNev]

Support to enable reusing the same plugin in different instances of AppInsights, owned by the same application (but using different Instrumentation keys) is required so that they can reuse a single Plugin instance for all instances.

Currently, while each AppInsights instance allows passing in extension plugins, internally this actually calls "initialize()" on each plugin for every instance, even if it's already been initialized.

Support for this requires 2 changes

• Add an optional isInitialized() method on the plugin interface so that a plugin is only initialized once
• Add an extra parameter to the processTelemetry() method so that singleton (shared) style plugins can access the current AppInsights instance/config without the need to save this during the initialize() call.

[MSNev]

Code is committed, will close the issue after we publish and official build (non-beta) with this change

[MSNev]

Version 2.4.3 is now published to CDN and NPM and addresses this enhancement

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.