Implement socks5 support

This adds following settings:

- Socks5Enabled
- Socks5Host
- Socks5Port
- Socks5User
- Socks5Password

Currently http requests and dns requests are not getting executed as they currently can't get tunneled through socks5 proxy. Therefore gmail with oauth2 wont work through tor.

deltachat-ffi/deltachat.h

@@ -271,6 +271,11 @@ char*           dc_get_blobdir               (const dc_context_t* context);
  * - `send_port`    = SMTP-port, guessed if left out
  * - `send_security`= SMTP-socket, one of @ref DC_SOCKET, defaults to #DC_SOCKET_AUTO
  * - `server_flags` = IMAP-/SMTP-flags as a combination of @ref DC_LP flags, guessed if left out
+ * - `socks5_enabled` = SOCKS5 enabled
+ * - `socks5_host` = SOCKS5 proxy server host
+ * - `socks5_port` = SOCKS5 proxy server port
+ * - `socks5_user` = SOCKS5 proxy username
+ * - `socks5_password` = SOCKS5 proxy password
  * - `imap_certificate_checks` = how to check IMAP certificates, one of the @ref DC_CERTCK flags, defaults to #DC_CERTCK_AUTO (0)
  * - `smtp_certificate_checks` = how to check SMTP certificates, one of the @ref DC_CERTCK flags, defaults to #DC_CERTCK_AUTO (0)
  * - `displayname`  = Own name to use when sending messages.  MUAs are allowed to spread this way e.g. using CC, defaults to empty

deltachat-ffi/src/lib.rs

@@ -3614,7 +3614,16 @@ pub unsafe extern "C" fn dc_provider_new_from_email(
         return ptr::null();
     }
     let addr = to_string_lossy(addr);
-    match block_on(provider::get_provider_info(addr.as_str())) {
+
+    let ctx = &*context;
+    let socks5_enabled = block_on(async move {
+        ctx.get_config_bool(config::Config::Socks5Enabled)
+            .await
+            .log_err(ctx, "Can't get config")
+            .unwrap_or_default()
+    });
+
+    match block_on(provider::get_provider_info(addr.as_str(), socks5_enabled)) {
         Some(provider) => provider,
         None => ptr::null_mut(),
     }