Repo Gardening: autolabel changes to Social previews in js package

Proposed changes:

Social Previews used to only live in their extension. That's no longer the case, so let's automate that.

Other information:

[ ] Have you written new tests for your changes, if applicable?
[ ] Have you checked the E2E test CI results, and verified that your changes do not break them?
[ ] Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

This can be tested in a fork. Merge this branch to trunk in your fork, then open a PR making changes to one of the files in the Social Previews component, e.g. projects/js-packages/publicize-components/src/components/social-previews/modal.js. Ensure that the Social Previews label is automatically added.

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Automattic / jetpack