add filename header for code blocks

Similar to gitbook, please add the ability to add a filename header to a code block.

Current outline code block example.
![image](


Gitbook example with a filename header.
![image](


This would take the form of perhaps an additional button in between where the code 'copy' button is, and the syntax selection dropdown.
![image](

Add a button that would add an additional tab at the top of the code block that would allow you to specify a filename, file path, or any other free text label for the code block.