[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/engines/spotify.py

@@ -5,9 +5,10 @@
 
 from json import loads
 from urllib.parse import urlencode
-import searx.poolrequests as requests
 import base64
 
+from searx.network import post as http_post
+
 # about
 about = {
     "website": 'https://www.spotify.com',
@@ -38,7 +39,7 @@ def request(query, params):
 
     params['url'] = search_url.format(query=urlencode({'q': query}), offset=offset)
 
-    r = requests.post(
+    r = http_post(
         'https://accounts.spotify.com/api/token',
         data={'grant_type': 'client_credentials'},
         headers={'Authorization': 'Basic ' + base64.b64encode(