tailcfg: add NodeCapMap

Like PeerCapMap, add a field to `tailcfg.Node` which provides
a map of Capability to raw JSON messages which are deferred to be
parsed later by the application code which cares about the specific
capabilities. This effectively allows us to prototype new behavior
without having to commit to a schema in tailcfg, and it also opens up
the possibilities to develop custom behavior in tsnet applications w/o
having to plumb through application specific data in the MapResponse.

Updates #4217

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/local.go

@@ -746,6 +746,13 @@ func (b *LocalBackend) UpdateStatus(sb *ipnstate.StatusBuilder) {
 				if c := sn.Capabilities(); c.Len() > 0 {
 					ss.Capabilities = c.AsSlice()
 				}
+				if cm := sn.CapMap(); cm.Len() > 0 {
+					ss.CapMap = make(tailcfg.NodeCapMap, sn.CapMap().Len())
+					cm.Range(func(k tailcfg.NodeCapability, v views.Slice[tailcfg.RawMessage]) bool {
+						ss.CapMap[k] = v.AsSlice()
+						return true
+					})
+				}
 			}
 			for _, addr := range tailscaleIPs {
 				ss.TailscaleIPs = append(ss.TailscaleIPs, addr)

ipn/ipnstate/ipnstate.go

@@ -258,6 +258,9 @@ type PeerStatus struct {
 	//    "funnel"
 	Capabilities []tailcfg.NodeCapability `json:",omitempty"`
 
+	// CapMap is a map of capabilities to their values.
+	CapMap tailcfg.NodeCapMap `json:",omitempty"`
+
 	// SSH_HostKeys are the node's SSH host keys, if known.
 	SSH_HostKeys []string `json:"sshHostKeys,omitempty"`
 
@@ -293,7 +296,7 @@ type PeerStatus struct {
 
 // HasCap reports whether ps has the given capability.
 func (ps *PeerStatus) HasCap(cap tailcfg.NodeCapability) bool {
-	return slices.Contains(ps.Capabilities, cap)
+	return ps.CapMap.Contains(cap) || slices.Contains(ps.Capabilities, cap)
 }
 
 // StatusBuilder is a request to construct a Status. A new StatusBuilder is