Event Lineage: Create Transform Function for Prefix Filter

[Cali0707]

Problem
Transform functions are how we track changes to eventtypes as events flow through the system. To support the prefix filter, we should implement a transform function to represent how a given eventtype becomes "narrower" as it passes the filter. Specifically, this transform function should (for each attribute set in the prefix filter):

1. Check if the attribute is already set. If it is and does not have the expected prefix from the filter, return a nil eventtype to model no events passing this filter
2. If the attribute is not already set, set it to the value expected by the filter, along with an empty variable for the suffix {x}.
3. If the attribute is compatible with the value required by the filter, but the filter provides more information, update the value to include the filter value. For example, if the value is currently ab{x}, where {x} is a variable, and the prefix filter is abc, then we can update the value to be abc{x}. Similarly, if the current value is {x}de, and the prefix filter is abc, then we can update the value to be abc{x}de.
4. If the prefix matches the value, but provides no new information, do not change anything. For example, if the value is abc, and the prefix is ab, then there is no need to make any change

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