TUN-8422: Add metrics for capnp method calls

Adds new suite of metrics to capture the following for capnp rpcs operations:
- Method calls
- Method call failures
- Method call latencies

Each of the operations is labeled by the handler that serves the method and
the method of operation invoked. Additionally, each of these are split
between if the operation was called by a client or served.

tunnelrpc/pogs/configuration_manager.go

@@ -8,10 +8,12 @@ import (
 	"zombiezen.com/go/capnproto2/rpc"
 	"zombiezen.com/go/capnproto2/server"
 
+	"github.com/cloudflare/cloudflared/tunnelrpc/metrics"
 	"github.com/cloudflare/cloudflared/tunnelrpc/proto"
 )
 
 type ConfigurationManager interface {
+	// UpdateConfiguration is the call provided to cloudflared to load the latest remote configuration.
 	UpdateConfiguration(ctx context.Context, version int32, config []byte) *UpdateConfigurationResponse
 }
 
@@ -24,6 +26,10 @@ func ConfigurationManager_ServerToClient(c ConfigurationManager) proto.Configura
 }
 
 func (i ConfigurationManager_PogsImpl) UpdateConfiguration(p proto.ConfigurationManager_updateConfiguration) error {
+	return metrics.ObserveServerHandler(func() error { return i.updateConfiguration(p) }, metrics.ConfigurationManager, metrics.OperationUpdateConfiguration)
+}
+
+func (i ConfigurationManager_PogsImpl) updateConfiguration(p proto.ConfigurationManager_updateConfiguration) error {
 	server.Ack(p.Options)
 
 	version := p.Params.Version()

tunnelrpc/pogs/registration_server.go

@@ -12,12 +12,18 @@ import (
 	"zombiezen.com/go/capnproto2/rpc"
 	"zombiezen.com/go/capnproto2/server"
 
+	"github.com/cloudflare/cloudflared/tunnelrpc/metrics"
 	"github.com/cloudflare/cloudflared/tunnelrpc/proto"
 )
 
 type RegistrationServer interface {
+	// RegisterConnection is the call typically handled by the edge to initiate and authenticate a new connection
+	// for cloudflared.
 	RegisterConnection(ctx context.Context, auth TunnelAuth, tunnelID uuid.UUID, connIndex byte, options *ConnectionOptions) (*ConnectionDetails, error)
+	// UnregisterConnection is the call typically handled by the edge to close an existing connection for cloudflared.
 	UnregisterConnection(ctx context.Context)
+	// UpdateLocalConfiguration is the call typically handled by the edge for cloudflared to provide the current
+	// configuration it is operating with.
 	UpdateLocalConfiguration(ctx context.Context, config []byte) error
 }
 
@@ -30,6 +36,10 @@ func RegistrationServer_ServerToClient(s RegistrationServer) proto.RegistrationS
 }
 
 func (i RegistrationServer_PogsImpl) RegisterConnection(p proto.RegistrationServer_registerConnection) error {
+	return metrics.ObserveServerHandler(func() error { return i.registerConnection(p) }, metrics.Registration, metrics.OperationRegisterConnection)
+}
+
+func (i RegistrationServer_PogsImpl) registerConnection(p proto.RegistrationServer_registerConnection) error {
 	server.Ack(p.Options)
 
 	auth, err := p.Params.Auth()
@@ -83,13 +93,18 @@ func (i RegistrationServer_PogsImpl) RegisterConnection(p proto.RegistrationServ
 }
 
 func (i RegistrationServer_PogsImpl) UnregisterConnection(p proto.RegistrationServer_unregisterConnection) error {
-	server.Ack(p.Options)
-
-	i.impl.UnregisterConnection(p.Ctx)
-	return nil
+	return metrics.ObserveServerHandler(func() error {
+		server.Ack(p.Options)
+		i.impl.UnregisterConnection(p.Ctx)
+		return nil // No metrics will be reported for failure as this method has no return value
+	}, metrics.Registration, metrics.OperationUnregisterConnection)
 }
 
-func (i RegistrationServer_PogsImpl) UpdateLocalConfiguration(c proto.RegistrationServer_updateLocalConfiguration) error {
+func (i RegistrationServer_PogsImpl) UpdateLocalConfiguration(p proto.RegistrationServer_updateLocalConfiguration) error {
+	return metrics.ObserveServerHandler(func() error { return i.updateLocalConfiguration(p) }, metrics.Registration, metrics.OperationUpdateLocalConfiguration)
+}
+
+func (i RegistrationServer_PogsImpl) updateLocalConfiguration(c proto.RegistrationServer_updateLocalConfiguration) error {
 	server.Ack(c.Options)
 
 	configBytes, err := c.Params.Config()

tunnelrpc/pogs/session_manager.go

@@ -11,6 +11,7 @@ import (
 	"zombiezen.com/go/capnproto2/rpc"
 	"zombiezen.com/go/capnproto2/server"
 
+	"github.com/cloudflare/cloudflared/tunnelrpc/metrics"
 	"github.com/cloudflare/cloudflared/tunnelrpc/proto"
 )
 
@@ -32,6 +33,10 @@ func SessionManager_ServerToClient(s SessionManager) proto.SessionManager {
 }
 
 func (i SessionManager_PogsImpl) RegisterUdpSession(p proto.SessionManager_registerUdpSession) error {
+	return metrics.ObserveServerHandler(func() error { return i.registerUdpSession(p) }, metrics.SessionManager, metrics.OperationRegisterUdpSession)
+}
+
+func (i SessionManager_PogsImpl) registerUdpSession(p proto.SessionManager_registerUdpSession) error {
 	server.Ack(p.Options)
 
 	sessionIDRaw, err := p.Params.SessionId()
@@ -78,6 +83,10 @@ func (i SessionManager_PogsImpl) RegisterUdpSession(p proto.SessionManager_regis
 }
 
 func (i SessionManager_PogsImpl) UnregisterUdpSession(p proto.SessionManager_unregisterUdpSession) error {
+	return metrics.ObserveServerHandler(func() error { return i.unregisterUdpSession(p) }, metrics.SessionManager, metrics.OperationUnregisterUdpSession)
+}
+
+func (i SessionManager_PogsImpl) unregisterUdpSession(p proto.SessionManager_unregisterUdpSession) error {
 	server.Ack(p.Options)
 
 	sessionIDRaw, err := p.Params.SessionId()