Add lowercase proxy vars and make priority consistent with other tools (

#16287)

* Add lowercase proxy vars and make priority consistent with other tools

* Add explanatory comments for lowercase vars

Co-authored-by: Jason Weill <93281816+JasonWeill@users.noreply.github.com>

---------

Co-authored-by: Jason Weill <93281816+JasonWeill@users.noreply.github.com>

jupyterlab/extensions/pypi.py

@@ -52,8 +52,12 @@ def make_connection(self, host):
 xmlrpc_transport_override = None
 
 all_proxy_url = environ.get("ALL_PROXY")
-http_proxy_url = environ.get("HTTP_PROXY") or all_proxy_url
-https_proxy_url = environ.get("HTTPS_PROXY") or all_proxy_url or http_proxy_url
+# For historical reasons, we also support the lowercase environment variables.
+# Info: https://about.gitlab.com/blog/2021/01/27/we-need-to-talk-no-proxy/
+http_proxy_url = environ.get("http_proxy") or environ.get("HTTP_PROXY") or all_proxy_url
+https_proxy_url = (
+    environ.get("https_proxy") or environ.get("HTTPS_PROXY") or http_proxy_url or all_proxy_url
+)
 proxies = None
 
 if http_proxy_url: