* Change generated documentation to indicate what image selection
options are required, and when.
* Refactor the structure of the documentation to highlight required
options for different types of builds
* builder/azure-arm: Update logic for setting subscriptionID
Previously, when using managed identities, the Azure builder would set the SubscriptionID in the Prepare method. But would not update it after getting the updated SubscriptionID from the metadata server. This change updates the Run method to ensure a valid subscriptionID is saved to the statebag before continuing with an image build.
Co-authored-by: Paul Meyer <paul.meyer@outlook.com>