Improve tkn chain log format

Prior to this commit, `tkn chain` logs look like:

```
$ tkn chains payload build-push-run-output-image-p229w
sync /dev/stderr: invalid argument
{"level":"info","ts":1654352100.0164135,"caller":"tekton/tekton.go:134","msg":"Retrieving payload on TaskRun default/build-push-run-output-image-p229w"}
{"level":"info","ts":1654352100.0164497,"caller":"tekton/tekton.go:86","msg":"Retrieving annotation \"chains.tekton.dev/payload-taskrun-6e2f020b-7d50-4022-8064-049680f72d32\" on TaskRun default/build-push-run-output-image-p229w"}
No payloads found for taskrun build-push-run-output-image-p229w
```

and after this commit they look like:

```
$ ./tkn chains payload build-push-run-output-image-p229w
sync /dev/stderr: invalid argument
Retrieving payload on TaskRun default/build-push-run-output-image-p229w
Retrieving annotation "chains.tekton.dev/payload-taskrun-6e2f020b-7d50-4022-8064-049680f72d32" on TaskRun default/build-push-run-output-image-p229w
No payloads found for taskrun build-push-run-output-image-p229w
```

which is more in line with how `tkn` logs look like in general.

pkg/chain/chain.go

@@ -17,6 +17,9 @@ package chain
 import (
 	"context"
 	"fmt"
+	"os"
+
+	"go.uber.org/zap/zapcore"
 
 	"github.com/tektoncd/chains/pkg/chains/storage"
 	"github.com/tektoncd/chains/pkg/config"
@@ -37,10 +40,12 @@ func ConfigMapToContext(cs *cli.Clients, namespace string) (context.Context, err
 
 func GetTaskRunBackends(cs *cli.Clients, namespace string, tr *v1beta1.TaskRun) (map[string]storage.Backend, config.StorageOpts, error) {
 	// Prepare the logger.
-	logger, err := zap.NewProduction()
-	if err != nil {
-		return nil, config.StorageOpts{}, err
+	encoderCfg := zapcore.EncoderConfig{
+		MessageKey: "msg",
 	}
+	core := zapcore.NewCore(zapcore.NewConsoleEncoder(encoderCfg), os.Stderr, zapcore.DebugLevel)
+	logger := zap.New(core).WithOptions()
+
 	// flushes buffer, if any
 	defer func() {
 		if err := logger.Sync(); err != nil {