Enhance ExecuteSQLQueryBuilder#validateScript() to allow chaining for multiple validations

[jklingen]

User story As a citrus user, I would like to be able to chain ExecuteSQLQueryBuilder#validateScript calls to add multiple validation scripts, so that each script (and resulting error message) is as distinct as possible.

Additional context Error messages are getting unwieldy when chaining script validations with &&. Also, we experienced that devs tend to expect validateScript to be chainable.