How to make a shipping method availability dependent on a custom configuration value?

You can programmatically manage a shipping carrier’s, method’s, or rate’s availability by implementing the following methods:

• \Magento\Shipping\Model\Carrier\AbstractCarrierInterface::isActive()
• \Magento\Shipping\Model\Carrier\CarrierInterface::getAllowedMethods()
• \Magento\Shipping\Model\Carrier\AbstractCarrierInterface::collectRates()