Remove translation from step_script to build_script in custom executor
### Overview
Remove the translation added in https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/2227 / https://gitlab.com/gitlab-org/gitlab-runner/-/issues/26418 for "step_script" to "build_script". Custom executor drivers would need to accept dynamically generated stage names, e.g. "step_script", "step_release".
As per the comment at https://gitlab.com/groups/gitlab-org/-/epics/6112#note_592485854, we should rollout this change in steps:
- [ ] Introduce an entry in the configuration structure that can be sent from the custom executor driver.
The entry will inform whether the driver supports `step_script` or not. When unset assume that custom executor driver expects `build_script`.
- [ ] Cchange the behavior to assume `step_script` expected by default.
The custom executor driver will need to explicitly define that `build_script` should be used.
- [ ] Remove support for `build_script`.
The follow job execution stage is going to be renamed:
| old stage name | new stage name |
|-|-|
| `build_script` | `step_script` |
epic