Optionally add msg.complete to split node output

[dceejay]

so can trigger join even when in manual mode. to address #4781

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

Proposed changes

This fix adds a checkbox to the split node to optionally add the msg.complete (true) flag to the last msg of the sequence sent from the split.

This is to address #4781, which flags a breaking change introduced by #4408 - which was an issue caused by the join node forcibly completing a join when in manual mode even when it wasn't wanted (as the parts property flagged that it was the last in the sequence) - But some users relied on this manual mode (mis-)behaviour and the change to make manual mean manual in #4408 has broken them.

By adding this option to add msg.complete - will force the join to complete - when the last item has been processed even in manual mode.

Checklist

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

[dceejay]

Closing this as #4796 is a better fix