Support dynamic variables in Flows Operations

[rijkvanzanten]

Describe the Improvement

This feels like an oversight. Dynamic variables aren't parsed properly when used in options like Filters for read-items. While $CURRENT_USER and $CURRENT_ROLE may or may not exist based on the trigger, variables like $NOW should universally be supported in flows.

Don't forget to revert #19869 when this issue is implemented :slig