add RESTler fuzzer to data validators

[marina-p]

Hello,

I noticed that ApiFuzzer is listed under validation tools, and wanted to suggest also adding the RESTler fuzzer to the list: https://github.com/microsoft/restler-fuzzer

RESTLER's description from the README:

RESTler is the first stateful REST API fuzzing tool for automatically testing cloud services through their REST APIs and finding security and reliability bugs in these services. For a given cloud service with an OpenAPI/Swagger specification, RESTler analyzes its entire specification, and then generates and executes tests that exercise the service through its REST API.

[matthewtrask]

hey that sounds good, if you open a PR we will get it merged. thanks!