codeintel-qa: Add clear command

Created by: efritz

Aids in #34900. This adds a clear command to the codeintel-qa command set which removes all index and upload records from the instance.

If applied prior to upload, it should put the instance in a "clean" state until we can do more work to make the query testing more resilient. It may take a bit more time to do this correctly, so this offers a partial solution to get the preprod workflows correct.

Test plan

N/A; is a test utility itself.