* collections: support toggling collections public/private, viewable via RWP
- backend: add 'public' to collection model, support patching to update
- backend: add .../collections/<id>/public/replay.json for public access
- backend: add CORS handling for public endpoint
- frontend: support 'make shareable / make private' dropdown actions on collection detail + collection list views
- frontend: show shareable / private icons by collection name on detail + list views
- frontend: link to replayweb.page for standalone browsing
- frontend: add embed code popup when a collection is shareable
- refer to public collections as 'shareable' for now
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Co-authored-by: Henry Wilkinson <henry@wilkinson.graphics>
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