Add a way to disable role assignments when using *AsExisting API

[davidfowl]

Discussed in #8051

^{Originally posted by DanielToft March 13, 2025}
Hi

I'm not sure I understand the purpose of RunAsExisting.

Why is it deploying role assignments to the resource for the user running the aspire project? If the user running the aspire project does not have access to the resources, the bicep script will also not have access to deploy the role assignments.

Is it possible to override this? I would like to have this feature, but I do not want all employees to have direct access to the resources. This will be impossible to control. We already have a model to give employees access to the right resources.

Today I'm using AddConnectionString, but I think it would be nice to have the resources shown in the dashboard as I would with RunAsExisting.