jobs: create per job configuration API

Currently, there are two general approaches for allowing the user to alter the configuration of a running job:
- create a cluster setting that gets checked during job execution. This has two main drawbacks: 1) the cluster setting affects all jobs that check that setting, instead of the specific executing job; 2) cockroach has way too many cluster settings (i.e. foot guns).
- create or modify a sql cmd along the lines of `ALTER {job} SET CONFIG {config}`. Currently c2c and backup schedules have this approach. The drawback is that its a pain to create and maintain a sql cmd for each type of job. Further, these current implementations manipulate details in the job record.

Instead of these approaches, we ought to create job config API, which allows a job writer to easily create and maintain an `ALTER {job_type} {job_id} SET CONFIG {config}` cmd variant. With this API, each job type would read and write its config information to the new job info table.

Jira issue: CRDB-33704

Epic CRDB-32494