Add ConvertTargetToSimpleJson for per-target conversion

[eyalk007]

This method allows converting a single TargetResults to SimpleJson format without flattening multiple targets together. Useful for tools like Frogbot that need to process each auto-detected target separately to maintain working directory associations when applying fixes.

• The pull request is targeting the dev branch.
• The code has been validated to compile successfully by running go vet ./....
• The code has been formatted properly using go fmt ./....
• All static analysis checks passed.
• All tests have passed. If this feature is not already covered by the tests, new tests have been added.
• Updated the Contributing page / ReadMe page / CI Workflow files if needed.
• All changes are detailed at the description. if not already covered at JFrog Documentation, new documentation have been added.

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[attiasas]

Feature will be included in here:

• Add option to only include specific targets in conversion #629