cmd/tailscale/cli,feature: add support for identity federation (#17529)

Add new arguments to `tailscale up` so authkeys can be generated dynamically via identity federation.

Updates #9192

Signed-off-by: mcoulombe <max@tailscale.com>

feature/buildfeatures/feature_identity_federation_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_identity_federation
+
+package buildfeatures
+
+// HasIdentityFederation is whether the binary was built with support for modular feature "Identity token exchange for auth key support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_identity_federation" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasIdentityFederation = false

feature/buildfeatures/feature_identity_federation_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_identity_federation
+
+package buildfeatures
+
+// HasIdentityFederation is whether the binary was built with support for modular feature "Identity token exchange for auth key support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_identity_federation" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasIdentityFederation = true