health, ipn/ipnlocal: add metrics for various client events (#15828)

updates tailscale/corp#28092

Adds metrics for various client events:
* Enabling an exit node
* Enabling a mullvad exit node
* Enabling a preferred exit node
* Setting WantRunning to true/false
* Requesting a bug report ID
* Profile counts
* Profile deletions
* Captive portal detection

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>

ipn/ipnlocal/node_backend.go

@@ -172,6 +172,17 @@ func (nb *nodeBackend) PeerByID(id tailcfg.NodeID) (_ tailcfg.NodeView, ok bool)
 	return n, ok
 }
 
+func (nb *nodeBackend) PeerByStableID(id tailcfg.StableNodeID) (_ tailcfg.NodeView, ok bool) {
+	nb.mu.Lock()
+	defer nb.mu.Unlock()
+	for _, n := range nb.peers {
+		if n.StableID() == id {
+			return n, true
+		}
+	}
+	return tailcfg.NodeView{}, false
+}
+
 func (nb *nodeBackend) UserByID(id tailcfg.UserID) (_ tailcfg.UserProfileView, ok bool) {
 	nb.mu.Lock()
 	nm := nb.netMap