Clarify supported expression operators and destination topic templating
Document that the expression language supports only the symbolic operators
(&&, ||, !) and that keyword forms (and, or, not) fail at runtime fail-closed,
so customers coming from SQL/KQL/Python get a clear pointer instead of a
cryptic parser error. Also clarify that only ${...} variables are substituted
in destination topics: a bare {field} is published literally, and arbitrary
payload fields can't be templated into the topic (use the data flow graph
${outputTopic} pattern instead).
ms.date bumped on both files.