Create BBM to backfill job environment records

Problem

Environments::Job records are now created for new jobs that use the environment keyword, and this table is now the source of truth for persisted environment options. However, old jobs that ran prior to this change still fetch their data from the metadata.

Proposal

Create a BBM to create Environments::Job records for historical jobs, using existing Ci::BuildMetadata records.

Implementation

Backfill job environments (!201868).

⚠️ this issue needs to be coordinated with Create BBM to migrate `ci_builds_metadata` into... (#552069) • Marius Bobin • 18.6 and other issues in the same epic ⚠️