Add a rule for Slowloris Attack

[ccojocar]

Summary

Add rule which should detect if ReadHeaderTimeout is configured in the http.Server. This should prevent a Slowloris Attack. See more details at https://medium.com/a-journey-with-go/go-understand-and-mitigate-slowloris-attack-711c1b1403f6.

[adamdecaf]

Wouldn't this check be more correct to alert when ReadTimeout == 0 and ReadHeaderTimeout == 0?

	// (snip) If ReadHeaderTimeout
	// is zero, the value of ReadTimeout is used. If both are
	// zero, there is no timeout.
	ReadHeaderTimeout [time](https://pkg.go.dev/time).[Duration](https://pkg.go.dev/time#Duration)

https://pkg.go.dev/net/http#Server.ReadHeaderTimeout

Edit: This appears to be used in Go 1.18.4 how the docs mention.