Add support for fuzz testing

Per [Wikipedia](https://en.wikipedia.org/wiki/Fuzzing):

> Fuzzing or fuzz testing is a software testing technique, often automated or semi-automated, that involves providing invalid, unexpected, or random data to the inputs of a computer program. The program is then monitored for exceptions such as crashes, or failing built-in code assertions or for finding potential memory leaks. Fuzzing is a form of random testing commonly used to test for security problems in software or computer systems.

Fuzz testing helps find hard-to-trigger bugs with less manual effort than via hand-written test cases. There are [various](http://www.guru99.com/fuzz-testing.html) [open-source](https://blackarch.org/fuzzer.html) [tools](https://www.peerlyst.com/posts/resource-open-source-fuzzers-list) for fuzz testing, but it's possible that we may need to write a custom tool that will provide randomly-generated but valid input for testing JanusGraph.

No files, tests, or entry points are identified. Start by reviewing JanusGraph's existing test setup and evaluating the referenced fuzzing tools; determine whether valid graph-input generation requires a custom tool. Done should mean fuzz testing is integrated and can exercise JanusGraph inputs.

Written by the indexing model from the issue text.