[Task]: improve Stream Schema Merge transform documentation

[bamaer]

What needs to happen?

If two fields with the same name but a different data type are found, the Stream Schema Merge converts the unified output field to a String:

hop/plugins/transforms/streamschemamerge/src/main/java/org/apache/hop/pipeline/transforms/streamschemamerge/SchemaMapper.java

Line 63 in c80693c

// check if we need to change the data type to string

This should be reflected in the documentation:
https://hop.apache.org/manual/latest/pipeline/transforms/streamschemamerge.html

Issue Priority

Priority: 3

Issue Component

Component: Documentation, Component: Transforms

[bamaer]

.take-issue