[Feature] Enable a callback to obtain the pageName as part of the analytics

[MSNev]

Suggested approach would be to move (or duplicate) the IValueCallback capability to the analytics extension

ApplicationInsights-JS/extensions/applicationinsights-clickanalytics-js/src/Interfaces/Datamodel.ts

Lines 113 to 121 in 3f96976

	/**
	* Value Callbacks configuration
	*/
	export interface IValueCallback {
	/**
	* Function to override the default pageName capturing behavior.
	*/
	pageName?: () => string;

This would enable a callback for SPA applications to programmatically derive the current page name.