New checker request: gnutls

New checker request: *gnutls*

**Source code**: https://gitlab.com/gnutls/gnutls

**CVEs**: https://www.cvedetails.com/vulnerability-list/vendor_id-72/product_id-4433/GNU-Gnutls.html

**Instructions**: [How to add a new checker to the CVE Binary Tool](https://github.com/intel/cve-bin-tool/blob/master/cve_bin_tool/checkers/README.md)