Make severity timing configurable

[liviakuenzli]

Sometimes we might want the severity to differ depending on the time of day or maybe the day of week or any other daterelated timing. For a application that is mainly used by customers during working hours it is critical that a certain API works whenever the customer does, but on the weekend it is not as critical.

[ravage84]

I guess, this is more of a documentation issue. I don't think we need to specifically implement this.

Instead of simply setting a literal severity, one can do two things:

1. Set a given severity depending on the date and/or time of the day in a simple if clause or ternary.
2. Set a callable, e.g. a closure.

Example for 1:

use \OrcaServices\Heartbeat\Heartbeat\Sensor;

$conditionalSeverity = Sensor::STATUS_NONCRITICAL;
if ($specialDateOrTimeOfDay) {
     $conditionalSeverity = Sensor::STATUS_CRITICAL;
}

$config['App']['Heartbeat'] = [
    'name' => 'My App',
    'layout' => 'heartbeat',
    'Sensors' => [
        'Sensor with conditional Severity' => [
            'enabled' => true,
            'severity' => $conditionalSeverity,
            'class' => Some\Sensor\Class,
        ],
    ],
];

Example for 2:

use \OrcaServices\Heartbeat\Heartbeat\Sensor;

$conditonalSeverity = function() use ($specialDateOrTimeOfDay) {
    if ($specialDateOrTimeOfDay) {
         return Sensor::STATUS_CRITICAL;
    }
    return Sensor::STATUS_NONCRITICAL;
};

$config['App']['Heartbeat'] = [
    'name' => 'My App',
    'layout' => 'heartbeat',
    'Sensors' => [
        'Sensor with conditional Severity' => [
            'enabled' => true,
            'severity' => $conditionalSeverity,
            'class' => Some\Sensor\Class,
        ],
    ],
];

We could put these examples in the configuration documentation.