Closes#53.

The linked issue was caused by a subtle difference in how we add paths to the server URLs in Go and Swift

In both languages, the (erroneous) urlhttps:/dev.coder.com is parsed the same:

• Scheme:https
• Host: "" /nil
• Relative Path:/dev.coder.com

However, in Swift, when we transform a server URL into a specific route on that server, such as/api/v2/users/me, we don't replace any existing part of the relative path, we just append to it, producinghttp:/dev.coder.com/api/v2/users/me, which gets sent, and the server responds to, just fine.

In Go, when we do the same transformation, we callsvrURL.Parse("/api/v2/users/me"), which replaces the existing relative path,/dev.coder.com, leading to the error in the linked issue, which has nodev.coder.com portion at all.

Previously, we were only ensuring that the link was a valid URL, and that the scheme washttps.
Now, we'll require that all server URLs have a host component. This meanshttp:/dev.coder.com fails to validate with a better error message.