feature/featuretags: add CacheNetMap feature tag for upcoming work

(trying to get in smaller obvious chunks ahead of later PRs to make
them smaller)

Updates #17925

Change-Id: I184002001055790484e4792af8ffe2a9a2465b2e
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/buildfeatures/feature_cachenetmap_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_cachenetmap
+
+package buildfeatures
+
+// HasCacheNetMap is whether the binary was built with support for modular feature "Cache the netmap on disk between runs".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_cachenetmap" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasCacheNetMap = false

feature/buildfeatures/feature_cachenetmap_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_cachenetmap
+
+package buildfeatures
+
+// HasCacheNetMap is whether the binary was built with support for modular feature "Cache the netmap on disk between runs".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_cachenetmap" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasCacheNetMap = true

feature/featuretags/featuretags.go

@@ -123,6 +123,10 @@ var Features = map[FeatureTag]FeatureMeta{
 		Desc:                 "Control-to-node (C2N) support",
 		ImplementationDetail: true,
 	},
+	"cachenetmap": {
+		Sym:  "CacheNetMap",
+		Desc: "Cache the netmap on disk between runs",
+	},
 	"captiveportal": {Sym: "CaptivePortal", Desc: "Captive portal detection"},
 	"capture":       {Sym: "Capture", Desc: "Packet capture"},
 	"cli":           {Sym: "CLI", Desc: "embed the CLI into the tailscaled binary"},