HPCC-32940 Allow keyed joins to conditional keys in roxie

[ghalliday]

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[github-actions]

Jira Issue: https://hpccsystems.atlassian.net//browse/HPCC-32940

Jirabot Action Result:
Assigning user: [email protected]
Workflow Transition To: Merge Pending
Updated PR

[ghalliday]

The logic was 95% coded, but there were several problems:

• The code generator did not support the right hand side being an IF() even though the logic was in roxie
• The code generator was using the wrong expression to determine the payload - which lead to payload fields being treated as keys (and failing)
• The roxie code did not work when files processed on the worker node.
• No test cases in the regression suite.

Richard, please review carefully, especially the change in ccdactivities.
I have targeted 9.6.x because it should not break any existing code, and it solves an immediate need, but up for discussion.