Detecting and filtering invalid environment names

[olegbespalov]

What?

Align the --include-system-env-vars with the --env in terms of the name validation.

In case of detecting an invalid name issue, the user will be warned.

 env -i 'LOREM-ISPUM=hello' IPSUM=lorem ./k6 run --include-system-env-vars samples/http_2.js

As the result, archive metadata should contain only IPSUM=lorem.

Why?

Closes: #2650