Add option pure_scp to SshOpts to allow scp to/from non unix systems

[richterger]

Add option pure_scp to SshOpts to allow scp to/from non unix systems

Description

Connecting to non unix system via scp fails, because pwd and ls are not available. The pure_scp option just disable anything and does only the pure scp transfer

Type of change

Please select relevant options.

• [X ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• [ X] My code follows the contribution guidelines of this project
• [ X] I have performed a self-review of my own code
• [ X] I have commented my code, particularly in hard-to-understand areas
• [ X] My changes generate no new warnings
• [ X] I formatted the code with cargo fmt
• [ X] I checked my code using cargo clippy and reports no warnings
• I have added tests that prove my fix is effective or that my feature works
• The changes I've made are Windows, MacOS, Linux compatible (or I've handled them using cfg target_os)
• I increased or maintained the code coverage for the project, compared to the previous commit

Acceptance tests

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• regression test: ...