Store published nodes json configuraton in Azure storage

[marcschier]

The feature adds the capability to download a storage volume as blob on startup using a connection string for blob storage. This will allow better fleet management of publishers.

The blob contains:

• publishednodes.json file
• initial pki folder structure including trust list, own cert and key
• ?

(all files are optional)

The blob is only downloaded if any of the files/folders do not exist locally. The blob and connection string to use are provided via command line argument.

The goal is to initialize a fresh publisher with initial configuration on startup and overcome IoT Hub Device twin size limitations. If there is no persistent volume locally, the files do not exist and so publisher will download every time it starts. If publisher cannot connect to Azure storage on startup it will wait until it can and no data will flow. If previously sending data using a blob pn.json file, this will lead to data loss. It is therefore recommended to still use volume mount to persist locally across publisher restarts rather than solely relying on this feature..

Support for uploading changes to the above files is out of scope of this feature.