Introduce fuzzy testing on Beats

> Fuzzing is a type of automated testing which continuously manipulates inputs to a program to find bugs. Go fuzzing uses coverage guidance to intelligently walk through the code being fuzzed to find and report failures to the user.

Go recently [introduced native support for Fuzzing](https://go.dev/security/fuzz/) as part of the `testing` package. We should start using it, the sooner we add it to our codebase with clear example/guides on how to use it, the easier it will be for anyone adding new tests to also use fuzzing where it makes sense.

We recently had some bugs in the TCP and UDP inputs that could have been caught by fuzzy-testing some of the functions used by those inputs.

Here is a couple of functions from those inputs that we could fuzzy-test to ensure they never panic:
https://github.com/elastic/beats/blob/f15240f0a326655842a659eed2cefd1c34d8a1f0/filebeat/input/udp/input.go#L318-L369

https://github.com/efd6/beats/blob/6dd570fb97c0a14ce902f788d90fb29fb099babe/filebeat/input/tcp/input.go#L296-L313