[mod] limiter: trusted proxies (#4911)

Replaces `x_for` functionality with `trusted_proxies`. This allows defining
which IP / ranges to trust extracting the client IP address from X-Forwarded-For
and X-Real-IP headers.

We don't know if the proxy chain will give us the proper client
address (REMOTE_ADDR in the WSGI environment), so we rely on reading the headers
of the proxy before SearXNG (if there is one, in that case it must be added to
trusted_proxies) hoping it has done the proper checks. In case a proxy in the
chain does not check the client address correctly, integrity is compromised and
this should be fixed by whoever manages the proxy, not us.

Closes:

- https://github.com/searxng/searxng/issues/4940
- https://github.com/searxng/searxng/issues/4939
- https://github.com/searxng/searxng/issues/4907
- https://github.com/searxng/searxng/issues/3632
- https://github.com/searxng/searxng/issues/3191
- https://github.com/searxng/searxng/issues/1237

Related:

- https://github.com/searxng/searxng-docker/issues/386
- https://github.com/inetol-infrastructure/searxng-container/issues/81

searx/botdetection/http_user_agent.py

@@ -20,8 +20,7 @@ from ipaddress import (
 )
 
 import werkzeug
-
-from searx.extended_types import SXNG_Request
+import flask
 
 from . import config
 from ._helpers import too_many_requests
@@ -56,7 +55,7 @@ def regexp_user_agent():
 
 def filter_request(
     network: IPv4Network | IPv6Network,
-    request: SXNG_Request,
+    request: flask.Request,
     cfg: config.Config,  # pylint: disable=unused-argument
 ) -> werkzeug.Response | None: