Feature: Add tooltip for activity Ratio in workspaces

[BekahHW]

Suggested solution

It can be unclear what Activity Ratio is, especially when it's low and the activity on repos is med-high. We should have a tooltip explaining activity ratio.

Ref: https://app.opensauced.pizza/workspaces/cbfb592d-2545-4e9c-a9c2-3edbb78cb562

Related: #1929

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