Is there a connector to call RESTful webservice just like the SAOP webservice connector ?
No.
Though you could develop one…see here:
http://documentation.bonitasoft.com/product-bos-sp/connectors
regards
Seán
PS: If this reply answers your question, please mark a resolved.
You can also call your RESTful webservice from a Groovy script.
You can then implement this groovy script in a Connector of type Script, or in an Operation.
You can find this contribution in the Community projects