backupccl: stress randomized tests in a nightly ci job

[msbutler]

Tests to consider:

• TestBackupRestoreRandomDataRoundtrips
• TestRandomParquetExports
• anything else?

Jira issue: CRDB-18951

[blathers-crl[bot]]

Hi @msbutler, please add a C-ategory label to your issue. Check out the label system docs.

While you're here, please consider adding an A- label to help keep our repository tidy.

_{:owl: Hoot! I am a Blathers, a bot for CockroachDB. My owner is otan.}

[blathers-crl[bot]]

cc @cockroachdb/bulk-io