feat!: constrain AppSettings.ENVIRONMENT

We are starting to amass a bit of functionality that is condition upon
the environment setting. E.g., sentry init disabled by default in
test and local environments, alternate logging config if environment is
local, and server reloading automatically configured for local
environment. So allowing this setting to be _anything_ doesn't make a
lot of sense.

Closes #244

src/starlite_saqlalchemy/settings.py

@@ -33,7 +33,7 @@ class Config:
     """Check for redis readiness on startup."""
     DEBUG: bool = False
     """Run `Starlite` with `debug=True`."""
-    ENVIRONMENT: str = "prod"
+    ENVIRONMENT: Literal["dev", "local", "prod", "stage", "test"] = "prod"
     """'dev', 'prod', etc."""
     NAME: str = "my-starlite-saqlalchemy-app"
     """Application name."""