Add API examples for C/C++

[engelmi]

Please describe what information you were trying to find

In #563, the structure for the BlueChi D-Bus API examples of bindings in different languages has been restructured. It would be great to add the missing examples in C/C++.

The C/C++ sample code files should be put into the following directory:
https://github.com/containers/bluechi/blob/main/doc/api-examples/c/

Checklist of missing examples:

• enable-unit
• get-cpuweight
• list-nodes
• list-node-units
• monitor-agent-connection
• monitor-node-connections
• monitor-unit
• set-cpuweight
• start-unit

The setup on how to run the examples has been written in the setup.md.

After adding all missing examples, the setup as well as all files can be linked in the doc/docs/api/examples.md.

[engelmi]

@dougsland Would you like to take this task? :)

[dougsland]

@dougsland Would you like to take this task? :)

if not urgent, sure thing. :)