add-on: integration of Device Configure

[joelguittet]

The purpose of this ticket is to integrate Device Configure API.

Tasks includes:

• rework of the artifact parser
• integration of the Device Configure API
• creation of the configure add-on (will be optional based on build configuration)
• update of examples to show the usage of the Device Configure API
• update of the documentation

The build of the Device Configure add-on the MCU must provides:

• option to include the add-on
• option to optionally save the configuration in the storage

The API of the Device Configure add-on the MCU must provides:

• initialization option to set refresh interval of the configuration with the server
• getter and setter of the device configuration to allow usage and modification of the device configuration from the application
• callback function to be informed of the device configuration when no storage is used

References:

• https://mender.io/product/features/device-configuration
• https://docs.mender.io/api/#device-api-device-configure