Add instrumentation and corresponding label to prioritization table

Why is this change being made?

We're putting an emphasis on instrumentation improvements and measurability, but we haven't defined the relative importance of this or a specific label we can use to keep track of these issues.

This MR incorporates instrumentation improvements (e.g. adding a counter to usage ping) and proposes that we start using the instrumentation label widely to make sure we can easily identify and track these issues.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per [say-why-not-just-what][transparency]
• Assign this change to the correct DRI
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