Backend: Serialize execution config into its own db record instead of storing in options col

The following discussion from !146333 (merged) should be addressed:

• @ayufan started a discussion: (+2 comments)

  This means that we will serialize this into options column. It would be better to introduce and use this to create execution_config object:

  execution_config: {
    run: job[:run]
  },
  options: {
  }

• discussion

  Can we ensure that for the same columns there's only one replica of this information? If we have 50 parallel jobs, we should use exactly one build_execution_config_id, or we have different jobs that use exact same content of build_execution_configs we could re-use.

More details about the proposal in !146333 (comment 1992575245)