Add dynamic favicon from API

[bookernath]

What/Why?

Uses new favicon node in GraphQL Storefront API to return the store's favicon dynamically. The API will always return something; if there's no favicon, it defaults to the BC logo.

I made this a static route because favicons change so infrequently, but this does mean you need to rebuild the app to see an updated favicon.

Rather than returning a <link> to our CDN, I'm proxying the image data and serving it directly; this is faster.

Putting do not merge on this until the new GraphQL node is fully rolled out.

Note: I tried to follow the pattern here and do this in an icon.ts file, but it didn't work for some reason.

Testing

Preview deployment: