Add Snowplow event for expanding security widget

What does this MR do?

Add Snowplow event for expanding security widget

• the defend/secure team wants to track how many users view the security report widget in merge requests
• added a new snowplow event to track the expansion of the widget
• ensured that it only tracked one event per load

Screenshots

New Snowplow event was emitted
only_one_event_720p

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 #218487 (closed)