feat: allow to capture command output to variable

[stesie]

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• Tests for the changes have been added (for bug fixes / features)
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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

So far it's a bit cumbersome if you want to capture the command output to a variable. The obvious work-around being redirecting stdout to a well-known temporary file, then using FORMULA type step in combination with inputFile and issue another command to delete the temporary file.

What is the new behavior?

You can specify resultVariable prop on the COMMAND type step, this will run the command with output capturing.

A subsequent FORMULA type step can the process the result further, e.g. split by newlines etc. to prepare entities for a select prompt etc.pp

Does this PR introduce a breaking change?

• Yes
• No

Other information

[MarcScheib]

Tested locally with an example use-case. Works really nice.