gocqlxtest: get config from env

[Ivan-Feofanov]

PR for the issue #247
With the replacement builtin flags package to github.com/namsral/flag we could take config as from flags so from env variables

[Gor027]

@avelanarius LGTM. Can you merge it?

[zimnx]

@Gor027 I don't think such little feature requires additional dependency (tagged as pre) to entire project. Keeping low subset of dependencies in libraries is a good thing. I'm against merging this.

[Gor027]

@zimnx I definitely agree with you, however, as it aims to be used for testing purposes only, perhaps it will not hurt to add it. I am not so familiar with Go, maybe there is a way to add a dependency for tests (or examples, or benchmarks) only, like [dev-dependencies] in Rust.

[zimnx]

Dependencies in Go are per module. Gocqlx consist of single module, so even test dependencies are part of library dependencies. This PR changes go.sum and go.mod of main module, so they are going into library dependencies.

[mmatczuk]

It's not worth adding another dependency for all users.

Having said that the Gocqlx core module could add some automation around env vars but it needs to be explicit (well defined function) and not use 3rd party libraries.