**What**
Add missing support for updating countries on the POST /admin/regions/:id route.
Furthermore, the PR refactors how the normalization and validation was handled in both create and update scenarios.
Finally, the PR adds a unique index on the country entity, which ensures at the DB level that we cannot have a duplicate country in the DB for a single region.
**What**
Add `POST /admin/regions`
Add `POST /admin/regions/:id`
Add `DELETE /admin/regions/:id`
All are added for v2 using API Routes and workflows.
In follow-up PRs, I will add support for passing countries in update and create.
Update: First follow-up PR is #6372
**What**
> [!NOTE]
> I can see this pr becoming huge, so I d like to get this partial one merged 👍
- Fixes shared connection usage (mikro orm compare the instance to its own package and therefore was resulting in not trully reusing the provided connection leading to exhausting the connection pool as multiple connections was created and end up not being all destroyed properly under the hood, discovered in my integration tests)
- Create shipping options method implementation
- DTO's definition and service interface update
- integration tests
- Re work of the indexes with new util update
- Test runner utils to remove a big chunk of the boilerplate of the packages integrations
FIXES CORE-1742
