Snowplow custom events for Monitor: APM

The intent is to instrument monitor dashboard related user activities. Out of a lot of things that need to be instrumented this MR specifically tracks the following:

1. If the user is loading a custom dashboard or default dashboard.
2. Number of charts that have data in a dashboard

category	action	label	property	value
projects:environments:metrics	dashboard_fetch	default_metrics_dashboard	count	number
projects:environments:metrics	dashboard_fetch	custom_metrics_dashboard	count	number

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• 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

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

This MR is the FE side of #34157 (closed)