Add Profinet diagnostics

[martinboers]

It would be useful to have a section showing how to access Profinet diagnostics, similar to Axioline diagnostics.
Sample code was given in an answer to this question in the PLCnext Community:
https://www.plcnext-community.net/forum/#/discussion/2621/accessing-profinet-controller-system-data-in-c-applications

[martinboers]

The example in Part 7 has now been updated to include Profinet diagnostics (thanks Marcus!).
This could be used in a new section, to show how to access Profinet IO and diagnostics.