Update Usage Ping Metrics Definitions - Grafana metrics

What does this MR do?

A tiny MVC for: #321812 (closed) to update the ping for Grafana metrics. This merge is part of a upcoming merge train to solve the validation for all related files in a batch approach outlined here: #321812 (comment 555415276)

Screenshots (strongly suggested)

No visual change.

Merge Train

What	Merge
Grafana metrics	🤘
Active prometheus metrics	TBA
Cluster metrics	TBA
Operations dashboard metrics	TBA
Alert metrics	TBA
SLA metrics	TBA
Tracing metrics	TBA

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 merge is ~"technical debt" reduction.
• [-] 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 #321812 (closed)