Allow passing custom HTTPClient to HTTPUpdate (#4959)

This enables customizing HTTP headers which adds some extra flexibility.
This does not break anything of course because this change introduces a new constructor with a new additional HTTPClient argument for HTTPUpdate class.

libraries/HTTPUpdate/src/HTTPUpdate.h

@@ -86,6 +86,10 @@ public:
 
     t_httpUpdate_return updateSpiffs(WiFiClient& client, const String& url, const String& currentVersion = "");
 
+    t_httpUpdate_return update(HTTPClient& httpClient,
+                               const String& currentVersion = "");
+
+    t_httpUpdate_return updateSpiffs(HTTPClient &httpClient, const String &currentVersion = "");
 
     int getLastError(void);
     String getLastErrorString(void);