Make use of `soft_delete` configurable

**Describe the Feature**
For development, being able to disable the soft-delete mechanism would be useful when testing behavior around deletions (e.g. #396).

**An Example**
An additional field it the API server configuration file (`src/config.default.toml`).
```
[dev]
disable_soft_delete=false
```
By default, it should be false, but it may be enabled when a direct hard deletes are preferred.

**Considered Alternatives**

Disabling it directly by modifying the code base:
- is harder to do, since you need to find and navigate to the correct line(s).
- if forgotten about and somehow merged in, is automatically deployed everywhere. Since `override` files are not in git, that risk is mitigated.

Setting it through an environment variable:
- the `.env` files are not API-specific, I'd prefer to keep API-only configurations to the dedicated configuration file as much as possible.

Setting it through the command line:
- currently requires editing the docker-compose file, which varies depending on the mode you are running (dev or not).

**Additional context**
I am still concerned with that it may accidentally be used in a production environment.
Perhaps we should add an additional check or variable which needs to be on to indicate a dev environment and quit out with an error if it is not set when hard deletes are enabled.