Make http(s) URIs their own module key (#495)

GenericUrl is a catch-all that uses URL.openConnection().
Since we now have special handling of HTTP urls, it makes more sense to
put it in its own module key.

pkl-cli/src/main/kotlin/org/pkl/cli/CliRepl.kt

@@ -45,6 +45,7 @@ internal class CliRepl(private val options: CliEvaluatorOptions) : CliCommand(op
             ModuleKeyFactories.fromServiceProviders() +
             listOf(
               ModuleKeyFactories.file,
+              ModuleKeyFactories.http,
               ModuleKeyFactories.pkg,
               ModuleKeyFactories.projectpackage,
               ModuleKeyFactories.genericUrl