Support specifying extra options for the CurlClient

[aik099]

Plan:

1. add array $extra_options = array() to the CurlClient:__construct method
2. in the CurlClient:__construct method store given $extra_options array into a new protected $extraOptions class property
3. in the CurlClient::sendRequest method use curl_setopt function to set $this->extraOptions to the current cURL connection

Motivation

This should cover the following use cases (maybe some future cases also):

• an ability to specify a proxy a proxy server (issue: Allow set proxy to use #194, pr: feat: set a proxy to use for the request #195) // cc: @aalcaidep
• an ability to specify connection timeout (issue: There should be an option to configure timeout with API #159, pr: Set timeout for fail gracefully #160) // cc: @ish1301