suggestion: Get resource existence

[WithHolm]

Is your feature request related to a problem? Please describe.
There are some times you want to just check if a resource exists before going ahead and modifying your current environment, a good example here would be to try to deploy a sql server with Entra/AAD admin only enabled.
When Entra/AAD admin only is enabled, you cannot set password when deploying a server that already exists.
It would result in a error like:

Conflict: Azure Active Directory Only Authentication is enabled. Please contact your system administrator. (Code:AadOnlyAuthenticationIsEnabled)

Describe the solution you'd like
I'm thinking that this would be handled in the same way that parameters are handled currently:

resource myresource 'resource/path@version' existing? {
 name: myresourcename
}

this way you could expect either a null value or a actual resource. later on you could choose to either deploy or not deploy specific settings depending on of the presence of current resources.

At this time, the only real option to do this is with deployscript, but if you have network policies enabled (like brownfield) this gets very complex, very fast for essenitally "is it there? ok les do this other thing instead". Concidering this operation is already a part of the arm api , i would assume this would be somewhat easy to implement and would not require any additional api changes within the exising ARM system.

[stephaniezyen]

Closing as duplicate of #4023