feat: configure edge function at route level

[kylesloper]

Unlike the Vercel adapter, the Netlify Adapter currently doesn't support route level config or specifying an edge function at the route level. (e.g) all routes are normal lambda functions but a specific route is rendered on the edge using export config .

I've used this internally for a while but thought it may be helpful to the wider community.

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[eltigerchino]

@kylesloper since you've been using this, has this allowed you to split your routes into both serverless and edge? Currently, the adapter has the limitation of only accepting the split config or edge config but not both. This PR would essentially be removing that limitation too, no?

I've tried uploading a build to Netlify and it only detects a single function although I have two routes, one configured with edge. I'm afraid we'd need to first solve the aforementioned issue and enable edge functions and split config to work with the adapter.