Explicitly allow or disallow extra keys in "component details" objects

[kalexmills]

Concerning the component details object, the current draft of this standard reads as:

On the value side of the equation, each "component details" object in the array MAY have one of the following object keys:

The definition of this object does not make explicit mention of any additional keys which may or may not be present. However, the example seems to include additional keys named node in the component detail object under checks['cpu:utilization']. It would be preferred to have an explicit statement allowing these keys, to ensure that implementations remain cross-compatible.