ipn/store: automatically migrate between plaintext and encrypted state (#16318)

Add a new `--encrypt-state` flag to `cmd/tailscaled`. Based on that
flag, migrate the existing state file to/from encrypted format if
needed.

Updates #15830

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

cmd/tsconnect/src/lib/js-state-store.ts

@@ -10,4 +10,7 @@ export const sessionStateStorage: IPNStateStorage = {
   getState(id) {
     return window.sessionStorage[`ipn-state-${id}`] || ""
   },
+  all() {
+    return JSON.stringify(window.sessionStorage)
+  },
 }

cmd/tsconnect/src/types/wasm_js.d.ts

@@ -44,6 +44,7 @@ declare global {
   interface IPNStateStorage {
     setState(id: string, value: string): void
     getState(id: string): string
+    all(): string
   }
 
   type IPNConfig = {