fix logging on config watcher setup failure

We have experienced an odd behaviour where argo-events would attempt to start
the eventsource pod, then exit just a few seconds later without producing any
meaningful error message. The process exit code was set to 1.

After some investigation and tracing the system calls, I found that the code
responsible for this is related to usage of the `viper` config parsing library.
Specifically, argo-events guards against bunch of possible errors while
initially reading in the configuration, but does not have necessary error
checking for setting up the file watchers. An example of such code can be found
here:

https://github.com/argoproj/argo-events/blob/78d47a2b6e948b9a3fa3572f0c95d8dcf5d7d8ff/eventbus/driver.go#L151

viper's `WatchConfig()` method will attempt to setup a watcher and if it's
unsuccesful, will log the error message and exit the process with code 1. The
trouble is that, by default the viper uses a discard logger so effectively log
message is never actually produced.

ref: https://github.com/spf13/viper/blob/8ac644165cf967d7d5be0cb149eb321c4c8ecfcf/viper.go#L446

An example of such execution in the Pod log files is not particularly easy to
troubleshoot.

Before the change:
```
$ ./argo-events-linux-arm64 eventsource-service
{"level":"info","ts":1710844334.7253304,"logger":"argo-events.eventsource","caller":"cmd/start.go:63","msg":"starting eventsource server","eventSourceName":"nautobot-webhook","version":"latest+78d47a2.dirty"}
{"level":"info","ts":1710844334.725548,"logger":"argo-events.eventsource","caller":"eventsources/eventing.go:454","msg":"Starting event source server...","eventSourceName":"nautobot-webhook"}
$
$ echo $?
1
$
```

After the change:

```
$ ./argo-events-linux-arm64 eventsource-service
{"level":"info","ts":1710844214.6256192,"logger":"argo-events.eventsource","caller":"cmd/start.go:63","msg":"starting eventsource server","eventSourceName":"nautobot-webhook","version":"latest+78d47a2.dirty"}
{"level":"info","ts":1710844214.6260495,"logger":"argo-events.eventsource","caller":"eventsources/eventing.go:454","msg":"Starting event source server...","eventSourceName":"nautobot-webhook"}
...
{"time":"2024-03-19T10:30:14.626883973Z","level":"ERROR","msg":"failed to create watcher: too many open files"}
$
```

This bug can be easily reproduced, ideally in separate VM by artificially
lowering the number of allowed `inotify` instances:

```
$ sudo sysctl fs.inotify.max_user_instances=0
$ ./argo-events-linux-arm64 eventsource-service
...
```

common/leaderelection/leaderelection.go

@@ -11,7 +11,6 @@ import (
 	"github.com/fsnotify/fsnotify"
 	"github.com/nats-io/graft"
 	nats "github.com/nats-io/nats.go"
-	"github.com/spf13/viper"
 	"go.uber.org/zap"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/client-go/kubernetes"
@@ -79,7 +78,7 @@ func getEventBusAuth(ctx context.Context, authStrategy *eventbusv1alpha1.AuthStr
 			Strategy: eventbusv1alpha1.AuthStrategyNone,
 		}
 	} else {
-		v := viper.New()
+		v := common.ViperWithLogging()
 		v.SetConfigName("auth")
 		v.SetConfigType("yaml")
 		v.AddConfigPath(eventBusAuthFileMountPath)

common/viper.go

@@ -0,0 +1,28 @@
+/*
+Copyright 2024 BlackRock, Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+	http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package common
+
+import (
+	"github.com/spf13/viper"
+	"log/slog"
+	"os"
+)
+
+func ViperWithLogging() *viper.Viper {
+	v := viper.NewWithOptions(viper.WithLogger(slog.New(slog.NewJSONHandler(os.Stdout, nil))))
+	return v
+}

controllers/config.go

@@ -4,8 +4,8 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/argoproj/argo-events/common"
 	"github.com/fsnotify/fsnotify"
-	"github.com/spf13/viper"
 )
 
 type GlobalConfig struct {
@@ -94,7 +94,7 @@ func (g *GlobalConfig) GetJetStreamVersion(version string) (*JetStreamVersion, e
 }
 
 func LoadConfig(onErrorReloading func(error)) (*GlobalConfig, error) {
-	v := viper.New()
+	v := common.ViperWithLogging()
 	v.SetConfigName("controller-config")
 	v.SetConfigType("yaml")
 	v.AddConfigPath("/etc/argo-events")

eventbus/driver.go

@@ -19,7 +19,6 @@ import (
 	stansensor "github.com/argoproj/argo-events/eventbus/stan/sensor"
 	eventbusv1alpha1 "github.com/argoproj/argo-events/pkg/apis/eventbus/v1alpha1"
 	"github.com/argoproj/argo-events/pkg/apis/sensor/v1alpha1"
-	"github.com/spf13/viper"
 )
 
 func GetEventSourceDriver(ctx context.Context, eventBusConfig eventbusv1alpha1.BusConfig, eventSourceName string, defaultSubject string) (eventbuscommon.EventSourceDriver, error) {
@@ -134,7 +133,7 @@ func GetAuth(ctx context.Context, eventBusConfig eventbusv1alpha1.BusConfig) (*e
 			Strategy: eventbusv1alpha1.AuthStrategyNone,
 		}
 	} else {
-		v := viper.New()
+		v := common.ViperWithLogging()
 		v.SetConfigName("auth")
 		v.SetConfigType("yaml")
 		v.AddConfigPath(common.EventBusAuthFileMountPath)