Add an insecure_disable_tls_host_verification command line option

When set, this disables the host verification of all HTTP requests. Available
for both the fetch and serve mode.

Also introduced an App.Config, for future command line options which need to
be passed more deeply into the code.

src/testing.zig

@@ -157,7 +157,7 @@ pub fn print(comptime fmt: []const u8, args: anytype) void {
 
 // dummy opts incase we want to add something, and not have to break all the callers
 pub fn app(_: anytype) *App {
-    return App.init(allocator, .serve) catch unreachable;
+    return App.init(allocator, .{.run_mode = .serve}) catch unreachable;
 }
 
 pub const Random = struct {