Make runtime label extraction opt-in

[srmagura]

Closes #2762.

I decided to document the new global flag, since I would be frustrated if my labels suddenly disappeared and there was nothing on our docs site about it.

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🦋 Changeset detected

Latest commit: c3c43fa

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@emotion/react	Minor

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Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 96.48%. Comparing base (f4640f6) to head (5591561).
Report is 50 commits behind head on main.

❗ Current head 5591561 differs from pull request most recent head c3c43fa

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Additional details and impacted files

Files	Coverage Δ
packages/react/src/emotion-element.js	94.66% <50.00%> (-5.34%)	⬇️

... and 10 files with indirect coverage changes

[scttcper]

@srmagura @Andarist would love to see this get merged as we'd like to disable stack based labels during tests and this would be an easy way to do that. Changes look good. Might consider making the flag true by default until the next major version though.

[mleibman-db]

Any traction on this?