New document "Considerations when migrating from existing bicep/arm templates"

[mahomedalid]

When we started to test ADE we did it using existing bicep/arm templates in our projects. I think that would be the natural journey of most of users of ADE, we had some lessons that would may be good to add to a new document, and that is the idea we want to discuss. Some of the items we though would be useful are:

• How to decide what group of resources constitute a catalog item, how to break your existing templates. We found out that the most natural way to break them are by resource-group (mainly because ADE creates a resource-group per environment), in other words, if your existing IaC has two resource groups, create one catalog item per resource group.
• How to manage secrets.
• If the bicep/arm templates are at subscription level (scope = subscription), they won't work, so, we need to break them in different catalog items, and do it at resource group level.
• Other considerations like naming standards, tags, etc. (probably a link to https://learn.microsoft.com/en-us/azure/cloud-adoption-framework/ready/azure-setup-guide/organize-resources)

[mahomedalid]

cc @renato-marciano @j-rewerts