support output redirection to a file in the CLI

`show joblog` may generate very long yarn job log, it is inconvenient to read such a long log in the CLI. But currently we do not have the capability to redirect the output to a file.

Look for the CLI command handling, likely in a source file like src/cmd or similar, focusing on the 'show joblog' command. Understand how output is currently printed to stdout. Add a flag or argument to redirect output to a file, using standard file I/O. Test by running the CLI with the new option and verifying the file is created with the job log content.

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