Add option for file-in node to include all properties (default off)

[dceejay]

and add test

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Add option to file-in node so when in per line or per chunk mode it will add all existing properties to the msg rather than creating a new one.. As this is a new feature it is targeted to dev.
To close Issue #3034

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality