all shells: Pass env vars through a key value store

[azr]

This potentially fixes #11197, by allowing to set shell env vars from a key/value map.

Merge hashicorp/packer-plugin-sdk#98 first.

• shell: add env key/value store possibility
• docs shell
• docs shell-local
• docs PowerShell
• docs windows shell
• docs shell-local-post-processor
• validation test
• build test
• build test on windows

[azr]

that's a neat feature for tests

[nywilken]

Nice little gem.

[nywilken]

This looks good to me. I do wonder if we should deprecate the environment_vars field.

[azr]

Good question, I would think not here, since for the people using environment_vars: this is not a new feature, but more like a bug fix and I bet a looooot of configs out there use this value.

On another side: these work with datasources, so it's way better 🤔 .

[github-actions]

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