Add config and functionality for integrating with Google Tag Manager

Purpose

This functionality will enable users to track app analytics using Google Tag Manager (GTM) instead of Google Analytics.

Implementation

We'll add a new config parameter called config_google_tag_manager_id or something similar. We'll integrate it into ConfigContext by setting it as part of the analytics object:

vectara-answer/src/contexts/ConfigurationContext.tsx

Lines 481 to 484 in d89576c

    
           setAnalytics({ 
        
             googleAnalyticsTrackingCode: config_google_analytics_tracking_code, 
        
             fullStoryOrgId: config_full_story_org_id, 
        
           });

Per guidance from @aamirbutt, we'll use https://www.npmjs.com/package/analytics to integrate with GTM.

Once we add it as a dependency, we can refer to these docs when integrating it into App.tsx, following the same pattern as the GA integration:

https://github.com/vectara/vectara-answer/blob/main/src/App.tsx#L24-L26

According to Aamir, we only need to initialize the integration in order for it to accomplish our primary goal of tracking an app visit:

Analytics({
  app: 'vectara-answer',
  plugins: [
    googleTagManager({
      containerId: 'GTM-123xyz'
    })
  ]
})

	setAnalytics({
	googleAnalyticsTrackingCode: config_google_analytics_tracking_code,
	fullStoryOrgId: config_full_story_org_id,
	});