fetch + serverName / SNI for https requests

[mrkurt]

In node land, we had some issues with fetch requests that weren't sending the right servername. This commit fixed it, I don't believe the Rust fetch implementation is doing this right yet: superfly/fly@de6aac5

superfly/fly is about to get an option to override servername in fetch that we'll need over here too.

[jeromegn]

Do we know if that's currently an issue?