Add CTA buttons & track their usage

What does this MR do?

Adds two CTA buttons to the informational popover related to the Highlight Paid Features During Active Trial experiment callout badge.

The two CTA buttons are:

1. “Upgrade to GitLab Premium” which opens a new tab with the in-app purchase flow page and auto-selects the group which has the active trial and the Premium plan
2. “Compare all plans” which opens a new tab with the billing page for the group which has the active trial

Screenshots

Before	After

How to test this locally

Please follow the directions from this MR.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because this experiment is behind a feature flag.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related to #327997 (closed)