…and Measure (#231)


This PR add a `Model` module to manage 
 - Asset: declare models and register metadata for them
 - Device: register metadata for device models
 - Measure: declare new measure types

Models can be registered on the framework with one of the `plugin.models.registerXXXX` method or at runtime with the `ModelController`:
 - writeAsset|Device|Measure: upsert a model
 - deleteAsset|Device|Measure: delete a model
 - listAsset|Device|Measure: list models

Decoder are now registered alongside with a Device model
```
deviceManager.models.registerDevice("DummyTemp", new DummyTempDecoder(), {
  color: { type: "keyword" },
});
```

----

Add default roles to manage plugin ressources. Admins roles can do everything and reader can only read.
 - `assets.admin`
 - `assets.reader`
 - `device.admin`: this role cannot attach and detach devices from engines
 - `device.reader`
 - `decoders.admin`
 - `measures.reader`
 - `measures.admin` 

 - device and asset models now have `defaultValues` for their metadata. Those values will be copied into assets and devices upon creation
 - fix bug that prevented metadata to be propagated and saved in measures collection

 --- 

Changes:

    measures document
    remove measure unit
    embedded measures
    measure names
    measures definition in digital twin models

Co-authored-by: Aschen <amaret@kuzzle.io>

…into 2-stable