Is your feature request related to a problem? Please describe.

We often want to look up jobs based on their type. It'd be great to index that.

Describe the solution you'd like

We should add a string column for the job type. On some level it'd be nice to make it a virtual computed column to extract the value from the proto. I worry that that might make writing job records more expensive because of the need to use crdb_internal.pb_to_json to express it.

Jira issue: CRDB-9346