Allow proper setCount SLAs across zones (#8752)

Fixes scenario where zones are appropriately
handled, along with supporting overriding set
count. The new fix also ensures that we handle
the various setup types properly.

Update documentation to properly indicate the
behavior.

Fixes #8750

Co-authored-by: Nitish Tiwari <nitish@minio.io>

cmd/object-api-errors.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"path"
@@ -429,14 +430,14 @@ func (e BackendDown) Error() string {
 
 // isErrBucketNotFound - Check if error type is BucketNotFound.
 func isErrBucketNotFound(err error) bool {
-	_, ok := err.(BucketNotFound)
-	return ok
+	var bkNotFound BucketNotFound
+	return errors.As(err, &bkNotFound)
 }
 
 // isErrObjectNotFound - Check if error type is ObjectNotFound.
 func isErrObjectNotFound(err error) bool {
-	_, ok := err.(ObjectNotFound)
-	return ok
+	var objNotFound ObjectNotFound
+	return errors.As(err, &objNotFound)
 }
 
 // PreConditionFailed - Check if copy precondition failed