[httpx] replace searx.poolrequests by searx.network

settings.yml:

* outgoing.networks:
   * can contains network definition
   * propertiers: enable_http, verify, http2, max_connections, max_keepalive_connections,
     keepalive_expiry, local_addresses, support_ipv4, support_ipv6, proxies, max_redirects, retries
   * retries: 0 by default, number of times searx retries to send the HTTP request (using different IP & proxy each time)
   * local_addresses can be "192.168.0.1/24" (it supports IPv6)
   * support_ipv4 & support_ipv6: both True by default
     see https://github.com/searx/searx/pull/1034
* each engine can define a "network" section:
   * either a full network description
   * either reference an existing network

* all HTTP requests of engine use the same HTTP configuration (it was not the case before, see proxy configuration in master)

searx/webapp.py

@@ -93,7 +93,7 @@ from searx.plugins import plugins
 from searx.plugins.oa_doi_rewrite import get_doi_resolver
 from searx.preferences import Preferences, ValidationException, LANGUAGE_CODES
 from searx.answerers import answerers
-from searx import poolrequests
+from searx.network import stream as http_stream
 from searx.answerers import ask
 from searx.metrology.error_recorder import errors_per_engines
 
@@ -919,7 +919,7 @@ def image_proxy():
     try:
         headers = dict_subset(request.headers, {'If-Modified-Since', 'If-None-Match'})
         headers['User-Agent'] = gen_useragent()
-        stream = poolrequests.stream(
+        stream = http_stream(
             method='GET',
             url=url,
             headers=headers,
@@ -1109,11 +1109,6 @@ def config():
     })
 
 
-@app.route('/config/http')
-def config_http():
-    return jsonify(poolrequests.debug_asyncclients())
-
-
 @app.errorhandler(404)
 def page_not_found(e):
     return render('404.html'), 404