Wrap errors from child workflow in canary sanity workflow (cadence-wo…

…rkflow#6279)

* Wrap errors from child workflow in canary sanity workflow

What changed?
Wrap errors when joining Child Workflows and joined all errors to sanity error

Why?
Previously only the last error from the child workflows was being set to sanity error, and it was not clear if the error was from a child workflow or from sanity workflow.

How did you test it?

Potential risks

Release notes

Documentation Changes

canary/sanity.go

@@ -21,7 +21,10 @@
 package canary
 
 import (
+	"fmt"
+
 	"go.uber.org/cadence/workflow"
+	"go.uber.org/multierr"
 	"go.uber.org/zap"
 )
 
@@ -94,6 +97,7 @@ func forkChildWorkflows(ctx workflow.Context, domain string, names []string) (wo
 		selector.AddFuture(future, func(f workflow.Future) {
 			if err := f.Get(ctx, nil); err != nil {
 				workflow.GetLogger(ctx).Error("child workflow failed", zap.Error(err))
+				err = fmt.Errorf("child workflow %s failed: %w", childName, err)
 				resultC.Send(ctx, err)
 				return
 			}
@@ -112,9 +116,7 @@ func joinChildWorkflows(ctx workflow.Context, names []string, selector workflow.
 		selector.Select(ctx)
 		var err1 error
 		resultC.Receive(ctx, &err1)
-		if err1 != nil {
-			err = err1
-		}
+		err = multierr.Append(err, err1)
 	}
 	return err
 }