[Feature Request] Release definition creation via Azure CLI

**Is your feature request related to a problem? Please describe.**
We have the ability to create Build definitions via Azure CLI via the `az pipelines create` command but no ability to create Release definitions. The 'az pipelines release create' command creates a new release within an existing definition, it does not allow creation of a new definition. This action is possible via REST API but not in Azure CLI natively.

**Describe the solution you'd like**
Either a new command specific to release definition creation or a parameter added to 'az pipelines create' that allows creation of either type of resource.

**Additional context**
Submitting a feature request was recommended on [this](https://devblogs.microsoft.com/devops/create-and-manage-azure-pipelines-from-the-command-line/) article.