Azure Storage account deployment with ARM

[Ravi-9654]

I want to deploy storage account using arm template. ARM template should handle below 2 cases.

If storage account not exists, create.
if storage account exists, don't create.
User wont pass any variable to ARM for storage account exists or not.

ARM should identify storage account exists or not, if not exists create storage account.

Issue Details
Repro steps (if necessary, delete otherwise)
Create template spec at subscription level to create storage account and blob ( if both not exists )
Validate template spec.
Deploy template spec.