jobs: add DELETE job ability

Customer Request: CANCEL JOB unfortunately leaves jobs behind to clutter up the jobs table until the jobs retention time is hit. Customer requested the ability to DELETE JOB, which would remove it as an entry in the jobs table. This way, they would be able to cancel jobs without them cluttering up the jobs table.

They want to keep their jobs retention time high for important jobs. However, they ran into an issue when testing changefeeds where they were constantly canceling changefeed jobs while testing, which quickly cluttered up the jobs table in a way that made the jobs table almost unusable. They would like to differentiate between types of job cancelations this way.

Jira issue: CRDB-28631