Rename diagnostic options to use kebab case

[nohwnd]

Describe the bug

--diagnostic-filelogger-synchronouswrite
--diagnostic-output-fileprefix

are not following the kebab case and put two words together. They should be renamed to

--diagnostic-filelogger-synchronous-write
--diagnostic-output-file-prefix

Or when put in context with the remaining logger option --diagnostic-output-directory

--diagnostic-output-write-file-synchronously

[MarcoRossignoli]

I'm fine with the rename.

[Evangelink]

I would even suggest

• --diagnostic-synchronous-write
• --diagnostic-file-prefix