Update priorities to include ~infradev and ~performance-grooming

Why is this change being made?

The Availability & Performance Grooming meeting takes place weekly, and engineering managers get assigned any outstanding issues that are not prioritized/scheduled. However, issues with those labels (~infradev and ~performance-grooming) are not officially a priority when compared to other labels such as ~availability, even though they are considered at the same or similar level of impact.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what