feat: external blocks homepage

[joshuaellis]

Why

• resolves #256

What

• adds the ability to add an External Card to the homepage array
• Makes changes to CardHome to accomodate this

Checklist

• [x] Ready to be merged

[vercel[bot]]

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Name	Status	Preview	Updated
companion-studio	✅ Ready (Inspect)	Visit Preview	Jun 1, 2022 at 4:00PM (UTC)