Enhance <exec> action with environment variables

[end2endzone]

Is your feature request related to a problem? Please describe.
There is no way to define a custom environment when starting a process with <exec> action.

Describe the solution you'd like
The <exec> action could be enhanced with the following child node:

<exec path="cmd.exe" wait="true" arguments="/k &quot;ffmpeg -version&quot;">
  <variable name="TEMP" value="c:\my-temp"/>
  <variable name="PATH" value="${env.PATH};c:\myapps\ffmpeg\bin"/>
</exec>

Describe alternatives you've considered
N/A

Additional context
N/A