Dumpling: dumpling will panic if --output-file-template is specified wrong

[lichunzhu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Run dumpling and specify a wrong output-file-template. For example,

run_dumpling --sql "select * from test.t" --filetype csv --output-filename-template "${TABLE_NAME}.${DB_NAME}.{{.index}}

2. What did you expect to see? (Required)

dumpling can report output-filename-template's error correctly.

3. What did you see instead (Required)

dumpling panics and quits.

4. What is your TiDB version? (Required)

v6.6.0