user stories:

• as a Golem creator, I'd like to know how I can pass environment variables to commands executed on the provider
• as an SDK team member, I'd like to confirm or deny the thesis: environment variables support works correctly

implementation details:

• use the env argument:
  https://github.com/golemfactory/yapapi/blob/master/yapapi/script/__init__.py#L154
• run e.g. /bin/sh -c set and check its output to verify that the command indeed sees the variable

outcomes:

• a new example in yapapi/examples folder which show users a way to set environment variables
• verify the relevant functionality works in yagna (vm runtime) -> as mentioned in create a simple yapapi example that passes an environment variable in a run command #1071 (comment) it possibly doesn't