[Feature Request] Ability to create, list, update and delete pipeline environments

| Command | Description |
|--- |--- |
|az pipelines environment create | Create an environment |
|az pipelines environment list | Show all environments in a project |
|az pipelines environment show | Show details of an environment |
|az pipelines environment delete | Delete an environment |
|az pipelines environment resource add | Add a resource to an environment |
|az pipelines environment resource list | List all the resources in an environment |
|az pipelines environment resource delete | Delete a resource in an environment |