chore(telemetry): measure "Add/edit note" on collection items

[caugner]

Summary

(MP-603)

Problem

We don't know how many users click on "Add note" or "Edit note" on the Collections page.

Solution

Add measurements.

Note: Also groups all Collections-related telemetry constants into a PLUS_COLLECTIONS object.

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How did you test this change?

Ran yarn && yarn dev with the following environment variables (in .env):

REACT_APP_GLEAN_DEBUG=true
REACT_APP_GLEAN_ENABLED=true

Then visited http://localhost:3000/en-US/plus/collections with a local Rumba and clicked on "Add note" and "Edit note" respectively.

[LeoMcA]

haven't tested, but I trust your testing - code changes look good