Add tracking for new merge request page

What does this MR do and why?

To better understand 'how' people are creating their first MR we need to fill in gaps in our tracking to be able to understand how people are arriving at the 'new merge request page'.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

• Sign in. Create public group with public project.
• Go to Merge requests. Click New merge request.
• Go to issues. Create public issue.
• Click Create merge request.
• Submit new merge request.
• Go to issues. Create private issue.
• Click Create confidential merge request.
• Go to Merge requests. Click New merge request in the header.
• Mare sure frontend events are generated:

activity	action
Create merge request on Issues	click_create_mr_issues_list
Create confidential merge request on Issues	click_create_confidential_mr_issues_list
New Merge request Button MR list	click_new_merge_request_list
New Merge Request CTA on MR empty state	click_new_merge_request_empty_list

Related to #437149 (closed)