Install-PSResource not adding Scripts install path to $env:PATH and allowing to invoke installed script

[anamnavi]

PR Summary

Installing a script with Install-PSResource happens successfully except that the script installation path (%USERPROFILE%\Documents\PowerShell\Scripts) isn't added to the environment PATH variable, so the script can't be invoked without prepending install folder path.

PR Context

Resolves #709 and was working in V2.

PR Checklist

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[alerickson]

V2 prompts for user to accept/confirm the action before setting the environment variable. I'm not a fan of prompts but since it's changing the env var, I think it might be important to include (see: https://github.com/PowerShell/PowerShellGetv2/blob/5aba7531f526b6e60b2757c36799995597b6dcec/src/PowerShellGet/PSGet.Resource.psd1#L222 for the v2 prompt)

[alerickson]

This looks good to me! Should be good once the tests are resolved.