editoast: create STDCM search env data model and CRUD

[Castavo]

Data Model

struct StdcmSearchEnvironment{
    infra_id: i64,
    electrical_profile_set_id: Option<i64>,
    work_schedule_group_id: Option<i64>,
    timetable_id: i64,
    simulation_window_begin: NaiveDateTime,
    simulation_window_end: NaiveDateTime
}

CRUD

• POST, for creation, delete existing envs.
• GET, no id, returns the latest object that exists, based on simulation_window_begin and end.
  If no object exists, returns a 500

We add a CLI to create an environment, and we add scripts like for railjson import and such.

How do we handle the fact that the env references other objects?

In the DB: forbid the deletion of the infra and timetable that are associated.
People will get 500s, it's okay, in the end it will be prevented by permissions added on objects if all goes well.