Add support for CA bundles (#885)

Why:

- Allow CA cert bundles to be used

This change addresses the need by:

- Adding a constructor that takes a pointer to the bundle
- Setting the WiFiClientSecure to use the bundle
- Adding an example

src/WebSocketsClient.h

@@ -53,6 +53,9 @@ class WebSocketsClient : protected WebSockets {
     void setSSLClientCertKey(const char * clientCert = NULL, const char * clientPrivateKey = NULL);
 #endif
     void beginSslWithCA(const char * host, uint16_t port, const char * url = "/", const char * CA_cert = NULL, const char * protocol = "arduino");
+#ifdef ESP32
+    void beginSslWithBundle(const char * host, uint16_t port, const char * url = "/", const uint8_t * CA_bundle = NULL, const char * protocol = "arduino");
+#endif
 #endif
 
     void beginSocketIO(const char * host, uint16_t port, const char * url = "/socket.io/?EIO=3", const char * protocol = "arduino");
@@ -112,6 +115,7 @@ class WebSocketsClient : protected WebSockets {
 #ifdef SSL_AXTLS
     String _fingerprint;
     const char * _CA_cert;
+    const uint8_t * _CA_bundle;
 #define SSL_FINGERPRINT_IS_SET (_fingerprint.length())
 #define SSL_FINGERPRINT_NULL ""
 #else