mobile: Update the Apple proxy settings polling to 10s

This is the same value that Cronet uses:
https://source.chromium.org/chromium/chromium/src/+/main:net/proxy_resolution/proxy_config_service_ios.cc;l=23;drc=0ddf755aab1e6d0f9c21fa09cd098c4ff6d1cac0.

Signed-off-by: Ali Beyad <abeyad@google.com>

mobile/library/common/network/apple_system_proxy_settings_monitor.cc

@@ -10,7 +10,7 @@ namespace Envoy {
 namespace Network {
 
 // The interval at which system proxy settings should be polled at.
-CFTimeInterval kProxySettingsRefreshRateSeconds = 7;
+CFTimeInterval kProxySettingsRefreshRateSeconds = 10;
 
 AppleSystemProxySettingsMonitor::AppleSystemProxySettingsMonitor(
     SystemProxySettingsReadCallback proxy_settings_read_callback)