Add collapse all button to "ARM Template Outline" side bar component

[Rabattkarte]

I really like the "ARM Template Outline" in my side bar. The only thing, I really miss is a button to collapse all elements again. Working with multiple resources, variables, parameters makes this really tedious if I have to collapse all elements again after opening many.

Please see the following two screenshots. One shows the way the HashiCorp Terraform extension handles this, and one shows vscode-azurearmtools:

Terraform:

Please notice the button marked in red.

ARM Tools:

Please add a button at the place of ‼️

[StephenWeatherford]

Released in https://github.com/microsoft/vscode-azurearmtools/releases/tag/v0.15.7 on 5/11.