Fix(eetrialbanner): fix EE trial banner to allow dismiss

What does this MR do?

A small MVC for #289925 (closed) where we allow the EETrialBanner to be dismissed after the parent class was changed from alert to gl-alert. To Fix this ~bug we change the helper to target any js-close actions on the banner and not the redundant close.bs.alert event we previously used. We also add supporting specs to ensure some test coverage for this update.

Screenshots (strongly suggested)

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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 #289925 (closed)