Working with golang modules

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Adding golang vendor modules

Project must have the go.mod created
```
go mod init
```

Use go get to add the package

GOPRIVATE=github.com/untangle/golang-shared go get -d github.com/untangle/golang-shared

Use go tidy to cleanup dependencies
```
go mod tidy
```
Use go vendor to add the vendor files into vendor/*
```
go mod vendor
```