Add view, dismissal, and submission events on 'GitLab is better with colleagues' modal

The purpose of this issue is to better understand the effectiveness of the 'GitLab is better with colleagues' modal that immediately appears post-registration. We want to add tracking to ensure we understand:

• How many of our new customers are seeing this modal
• How many of our new customers are dismissing this modal
• How many of our new customers are inviting users from this modal

Structured events to be added:

Notes (reference for this issue, not an actual snowplow event property)	category	action	label	Additional context to capture
Event fires when 'GitLab is better with colleagues' modal loads.	projects:learn_gitlab:index	render	invite_celebration_modal	GitLab User ID
Event fires when user "dismisses" i.e. User clicks continue on X or Cancel	projects:learn_gitlab:index	click_x or click_cancel	invite_celebration_modal	GitLab User ID
Event fires when user 'Invites' a colleague i.e. User clicks Invite	projects:learn_gitlab:index	click_invite	invite_celebration_modal	GitLab User ID

Implementation hints

• Look to utilize trigger_source/source as defined here.