jobs: record retriable errors in the job upon failure

[ajwerner]

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

The jobs Payload protobuf has a field for errors experienced during execution. We never populate it. Now that we have exponential backoff offered by the framework itself (which we needed to put there to deal with crashing), we will want information about why we're in that backoff loop.

This is also likely to justify creating a better error type to indicate retriability.

Epic: CRDB-7912