select: Check if CSV is valid utf8 (#10991)

Check if first block of data is valid utf8.

Fixes #10970

pkg/s3select/csv/errors.go

@@ -16,6 +16,8 @@
 
 package csv
 
+import "errors"
+
 type s3Error struct {
 	code       string
 	message    string
@@ -51,3 +53,12 @@ func errCSVParsingError(err error) *s3Error {
 		cause:      err,
 	}
 }
+
+func errInvalidTextEncodingError() *s3Error {
+	return &s3Error{
+		code:       "InvalidTextEncoding",
+		message:    "UTF-8 encoding is required.",
+		statusCode: 400,
+		cause:      errors.New("invalid utf8 encoding"),
+	}
+}