workload: add INSPECT to random schema workload

[spilchen]

Add an INSPECT operation to the random schema workload. While INSPECT isn’t a schema change, we want to observe how it behaves alongside schema changes and concurrent DML (mainly inserts).

Details

• Randomize between inspecting the whole database or a random table.
• Vary the AS OF timestamps used.
• Capture any INSPECT errors by running SHOW INSPECT ERRORS for each job at the end of the run. This makes debugging easier if issues occur.

Jira issue: CRDB-55452

Epic CRDB-55075