Make api key enablement configurable in runtime

[arbulu89]

Make api_key usage enabled option configurable in runtime. It will come handy for e2e testing scenarios.

PD:
The other option was to provide the option to use a configurable api_key base value, but we decided to not implement this, as the current api_key implementation is not that good, and we might change it at some point, so going with the easy disable option was preferred. In any case, the api_key depends on the secret_key_base, so both this and the custom api_key should be fixed to have a unique key

[arbulu89]

@fabriziosestito At the end, I have changed strategy 😅
We cannot change a variable that was fetched during compilation (compile_env).
I have opted to go with unplug as we do with wanda so we can enable/disable phoenix plugs on demand with runtime changes.
This time I tested properly and it works 🐰