Add FTM support and examples (#5272)

Rework of #5266 by @pedrominatel

libraries/WiFi/examples/FTM/FTM_Responder/FTM_Responder.ino

@@ -0,0 +1,23 @@
+/* Wi-Fi FTM Responder Arduino Example
+
+  This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+  Unless required by applicable law or agreed to in writing, this
+  software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+  CONDITIONS OF ANY KIND, either express or implied.
+*/
+#include "WiFi.h"
+// Change the SSID and PASSWORD here if needed
+const char * WIFI_FTM_SSID = "WiFi_FTM_Responder";
+const char * WIFI_FTM_PASS = "ftm_responder";
+
+void setup() {
+  Serial.begin(115200);
+  Serial.println("Starting SoftAP with FTM Responder support");
+  // Enable AP with FTM support (last argument is 'true')
+  WiFi.softAP(WIFI_FTM_SSID, WIFI_FTM_PASS, 1, 0, 4, true);
+}
+
+void loop() {
+  delay(1000);
+}