It's a new provider that provides virtual machines on Grid'5000.

Example:

```
conf = Configuration.from_settings(job_name="tuto-vmong5k")\
    .add_machine(roles=["control"],
                 cluster="parapluie",
                 number=3,
                 flavour="large")\
    .add_machine(roles=["compute"],
                 cluster="parapluie",
                 number=100,
                 flavour="tiny")\
    .finalize()
provider = VMonG5k(conf)

roles, networks = provider.init()

```

It adds a new `enos_vmong5k` package alongside new modules:

- `enos_vmong5k.configuration`
- `enos_vmong5k.schema`
- `enos_vmong5k.constants`
- `enos_vmong5k.provider`

and also new unit tests and documentation (functionnal tests in
docs/tutorials/vmong5k)

The VmonG5K provider internally uses the G5k provider. In particular it sets
the job_type to allow_classic_ssh and claim an extra slash_22 subnet.