Fix type hinting for load_env (#2107)

* Deprecate `load_env` in favor of `env_prefix`

`load_env` both enabled/disabled environment variable parsing, while
also letting the user modify the env prefix. Deprecate the ability to
disable environment parsing, and add a new config variable to track the
user's desired prefix for environment-based configuration.

Resolves: #2102

* Add a few common .gitignore patterns

tests/test_keep_alive_timeout.py

@@ -1,4 +1,5 @@
 import asyncio
+import platform
 
 from asyncio import sleep as aio_sleep
 from json import JSONDecodeError
@@ -6,7 +7,6 @@ from os import environ
 
 import httpcore
 import httpx
-import platform
 import pytest
 
 from sanic_testing.testing import HOST, SanicTestClient