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

**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.

Start at ExecuteSQLQueryBuilder#validateScript and inspect how repeated calls are currently handled. Verify that multiple calls can be chained, that each validation script remains distinct, and that each resulting error message is separate.

Written by the indexing model from the issue text.