esp_websocket_client: Add websocket client component

Closes https://github.com/espressif/esp-idf/issues/2829


* Original commit: espressif/esp-idf@2a2d932cfe

docs/en/api-reference/protocols/esp_websocket_client.rst

@@ -0,0 +1,70 @@
+ESP WebSocket Client
+====================
+
+Overview
+--------
+The ESP WebSocket client is an implementation of `WebSocket protocol client <https://tools.ietf.org/html/rfc6455>`_ for ESP32
+
+Features
+--------
+   * supports WebSocket over TCP, SSL with mbedtls
+   * Easy to setup with URI
+   * Multiple instances (Multiple clients in one application)
+
+Configuration
+-------------
+URI
+^^^
+
+-  Supports ``ws``, ``wss`` schemes
+-  WebSocket samples:
+
+   -  ``ws://websocket.org``: WebSocket over TCP, default port 80
+   -  ``wss://websocket.org``: WebSocket over SSL, default port 443
+  
+-  Minimal configurations:
+
+.. code:: c
+
+    const esp_websocket_client_config_t ws_cfg = {
+        .uri = "ws://websocket.org",
+    };
+
+-  If there are any options related to the URI in
+   ``esp_websocket_client_config_t``, the option defined by the URI will be
+   overridden. Sample:
+
+.. code:: c
+
+    const esp_websocket_client_config_t ws_cfg = {
+        .uri = "ws://websocket.org:123",
+        .port = 4567,
+    };
+    //WebSocket client will connect to websocket.org using port 4567
+
+SSL
+^^^
+
+-  Get certificate from server, example: ``websocket.org``
+   ``openssl s_client -showcerts -connect websocket.org:443 </dev/null 2>/dev/null|openssl x509 -outform PEM >websocket_org.pem``
+-  Configuration:
+
+.. code:: cpp
+
+    const esp_websocket_client_config_t ws_cfg = {
+        .uri = "wss://websocket.org",
+        .cert_pem = (const char *)websocket_org_pem_start,
+    };
+
+For more options on ``esp_websocket_client_config_t``, please refer to API reference below
+
+Application Example
+-------------------
+Simple WebSocket example that uses esp_websocket_client to establish a websocket connection and send/receive data with the `websocket.org <https://websocket.org>`_ Server: :example:`protocols/websocket`.
+
+
+API Reference
+-------------
+
+.. include:: /_build/inc/esp_websocket_client.inc
+