As a dev, I want to simplify the usage of `sub_type` in `fertiscan`

## Description

**Context**
Currently, the `sub_type` table is defined with fields `type_fr` and `type_en` as unique text columns. However, we never actually use `type_fr` in practice. The `sub_type` is being used more like an enum. After schema creation, we have to perform separate `sub_type` inserts to populate this table, which is necessary for the database design to be usable.


**Problem Statement**
The need to perform separate `sub_type` inserts after schema creation adds unnecessary complexity to our setup and deployment processes. This approach has several drawbacks:

- **Increased Setup Complexity**: Additional scripts or manual steps are required to insert initial data, which can be error-prone.
- **Deployment Challenges**: Ensuring that the inserts run in the correct order and environment adds overhead.
- **Maintenance Overhead**: Keeping track of initial data inserts complicates version control and collaboration.

By using an enum instead of a table for `sub_type`, we can simplify the schema and eliminate the need for post-creation data inserts.

## Acceptance Criteria
- Evaluate the feasibility and benefits of replacing the `sub_type` table with an enum.
- Implement the enum to replace the `sub_type` table if it leads to simplification.
- Remove the need for separate `sub_type` inserts after schema creation.
- Ensure that existing functionality dependent on `sub_type` remains unaffected.