Previously the location the file was uploaded to was set internally and
used ${env:SYSTEMROOT}/Temp as the destination folder.
By default, in order to inject the required environment variables, the file
is 'dot sourced' by the 'execute_command' using the {{ .Vars }} variable.
Unfortunately the inclusion of the dollar in the path caused issues for
users connecting over ssh as the (typically bash) shell running the execute
command would try and interpret the dollar sign.
The change allows users to specify the location the file is uploaded to,
thereby allowing the user to specify a custom 'execute_command' that
escapes any dollar signs that could be present in the path.
If not set the upload path now defaults to using C:/Windows/Temp as the
upload folder.
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