fix: go version not properly identified in binary

[kzantow]

This PR corrects an issue identifying the version string in go binaries. The binary may contain many matching go#.# patterns, for example in help text strings that may be presented to the user. These may occur before the actual version string. This PR attempts to find the correct version string by searching for <pattern><NULL>, which upon inspecting the go binary seems to be one of the only ways to identify it.

This PR also corrects a missing FoundBy field as well as the CPE used for the Go binary.

Fixes #1382

FWIW I've run this on my local macOS go binary, as well as the latest docker images through 1.16:

% syft file:/usr/local/go/bin/go
go    1.18     binary  

% syft golang:1.19 | grep go    
go                         1.19.3                          binary  
libgomp1                   10.2.1-6                        deb     

% syft golang:1.18 | grep go
go                         1.18.8                          binary  
libgomp1                   10.2.1-6                        deb     

% syft golang:1.17 | grep go
go                         1.17.13                         binary  
libgomp1                   10.2.1-6                        deb     

% syft golang:1.16 | grep go
go                         1.16.15                         binary  
libgomp1                   10.2.1-6                        deb