Added support for probes in configuration

[AlbertoSH]

Sample of how the configuration could look like

    {
        "cert": "/some/path/file.crt",
        "token": {
            "type": "env",
            "key": "MY_TOKEN"
        },
        "date": {
          "type": "probe",
          "name": "Current date",
          "provider": {
            "type": "process",
            "path": "date"
          }
        },
        "words": {
          "type": "probe",
          "name": "Some capped words",
          "provider": {
              "type": "python",
              "module": "string",
              "func": "capwords",
              "arguments": {
                "s": "some words"
              }
          }
        },
        "valueFromServer": {
          "type": "probe",
          "name": "Some value taken from the network",
          "provider": {
            "type": "http",
            "url": "http://my.config.server.com/value"
         }
        }
    }

[codecov-io]

Codecov Report

Merging #123 into master will decrease coverage by 0.02%.
The diff coverage is 72.72%.

@@            Coverage Diff             @@
##           master     #123      +/-   ##
==========================================
- Coverage   83.24%   83.22%   -0.03%     
==========================================
  Files          23       23              
  Lines        1570     1580      +10     
==========================================
+ Hits         1307     1315       +8     
- Misses        263      265       +2

Impacted Files	Coverage Δ
chaoslib/configuration.py	89.65% <72.72%> (-10.35%)	⬇️
chaoslib/provider/process.py	95.55% <0%> (+2.22%)	⬆️

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[Lawouach]

Thanks a lot for the kicking the discussion on this one.

I'm going to take some time to think about it because it's not a small change nor a small thing to support. So, I will have to ask patience if you don't mind as I'm always quite careful about changing the core :)

[AlbertoSH]

Sure! Implementation-wise, it's not a big deal but a change of this nature could introduce some problems at the specification level
So yes, take your time ;)
In the meantime and for my purposes, I can use my version

Potentially, a new kind of probe (configuration-probe) could be added just for configuration purposes. That would allow us to define what we need the way we need without the issues of using something that's already there (and compatibility needs to be maintained). Something like

{
        "cert": "/some/path/file.crt",
        "token": {
            "type": "env",
            "key": "MY_TOKEN"
        },
        "date": {
          "type": "configuration-probe",
          "provider": {
            "type": "process",
            "path": "date"
          }
        },
        "words": {
          "type": "configuration-probe",
          "provider": {
              "type": "python",
              "module": "string",
              "func": "capwords",
              "arguments": {
                "s": "some words"
              }
          }
        },
        "valueFromServer": {
          "type": "configuration-probe",
          "provider": {
            "type": "http",
            "url": "http://my.config.server.com/value"
         }
        }
    }

In the end, whatever allows us to compute a value at runtime would be enough

[Lawouach]

Hi there,

I haven't forgotten about this PR. Just was busy elsewhere unfortunately :(