jobsprofiler: execution detail files should contain the collectedAt timestamp and file type

Recently, we added support for different parts of the system to generate and persist execution detail files describing the state of the job. Currently the naming convention of these files is up to the caller. We should enforce a naming convention that includes the timestamp at which the file was collected, as well as the type of the file being persisted. This will make it easier to display the timestamp in the job details page and set the current `Content-type` when triggering a download of the file.

Epic: CRDB-8964

Jira issue: CRDB-29928