Small tweaks to Holocene components for self serve signup

[rossedfort]

Description & motivation 💭

• Support label slot in checkbox. This is so that links (or any other markup) can be rendered in the checkbox label

• Add close event to combobox. This is so that we have an event to catch when the menu is closed without the user having selected a value (i.e. they open the list of options by focusing the combobox, but then click away). This is useful to add inline errors to the combobox when a value is required.
• Only dispatch close even from <MenuContainer /> if menu is open

Screenshots (if applicable) 📸

Design Considerations 🎨

Testing 🧪

How was this tested 👻

• Manual testing
• E2E tests added
• Unit tests added

Steps for others to test: 🚶🏽‍♂️🚶🏽‍♀️

Checklists

Draft Checklist

Merge Checklist

Issue(s) closed

Docs

Any docs updates needed?

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Name	Status	Preview	Updated (UTC)
holocene	✅ Ready (Inspect)	Visit Preview	Feb 14, 2024 5:35pm

[laurakwhit]

Could a checkbox potentially have both a label slot and a label prop? Wondering if we want to make this a conditional so that there's no potential for both.