ipn: add WebServerConfig, add views

cmd/viewer couldn't deal with that map-of-map. Add a wrapper type
instead, which also gives us a place to add future stuff.

Updates tailscale/corp#7515

Change-Id: I44a4ca1915300ea8678e5b0385056f0642ccb155
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/doc.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:generate go run tailscale.com/cmd/viewer -type=Prefs,ServeConfig,TCPPortHandler,HTTPHandler,WebServerConfig
+
 // Package ipn implements the interactions between the Tailscale cloud
 // control plane and the local network stack.
 //