Draft: Add new operational support for services

[rical]

Description

Augment new services container to ietf-system

This patch adds operational data support for system services. The data is in a generic format but is intended to be able to represent finit information (initctl) nicely.

The reason for augmenting this to ietf-system and not to infix-services is that we consider this generic system information which is totally disconnected from what ever services infix might provide.

In this first state we only support pid, name, description and state. Making the data look something like:

"ietf-system:system-state": {                                                                                                                                                                                                           
    "infix-system:services": {                                                                                                                                                                                                            
      "service": [                                                                                                                                                                                                                        
        {                                                                                                                                                                                                                                 
          "pid": 1187,                                                                                                                                                                                                                    
          "name": "udevd",                                                                                                                                                                                                                
          "description": "Device event daemon (udev)",                                                                                                                                                                                    
          "status": "running"                                                                                                                                                                                                             
        },

Checklist

Tick relevant boxes, this PR is-a or has-a:

• [ ] Bugfix
  • [ ] Regression tests
  • [ ] ChangeLog updates (for next release)
• [x] Feature
  • [x] YANG model change => revision updated?
  • [x] Regression tests added?
  • [ ] ChangeLog updates (for next release)
  • [ ] Documentation added?
• [ ] Test changes
  • [ ] Checked in changed Readme.adoc (make test-spec)
  • [ ] Added new test to group Readme.adoc and yaml file
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (please detail in commit messages)
• [ ] Build related changes
• [ ] Documentation content changes
  • [ ] ChangeLog updated (for major changes)
• [ ] Other (please describe):