`tsh request search` should support `--format`

[programmerq]

What would you like Teleport to do?

tsh request search doesn't currently support -f, --format Format output (text, json, yaml, names).

This command should support the same formats that tsh ls, tsh db ls, tsh kube ls, etc all support.

What problem does this solve?

This will help power users, and make the tsh experience more uniform.

If a workaround exists, please include it.

There isn't a great workaround since the request search is different than what tctl get or those other tsh <command> ls commands do. Parsing the table output is not great.