Prevent redundant title front-matter property

[g-pavlov]

What would you like to be added:
Use the document front matter if it is available and the node-defined front matter only if it is not in preparation for a more thorough implementation with merge strategies.

Why is this needed / describe a real-world scenario:
If there is front matter in a document and in the node that has source referencing this document, currently it is concatenated as two sequential byte data streams and that leads to potentially redundant properties.

How to categorize this?:
/kind enhancement
/priority critical