Design UX for creating workloads with projects selected in top nav

[catherineluse]

This issue is a follow-up to https://github.com/rancher/dashboard/issues/6094

In the above linked issue, it has been requested to narrow down the list of namespaces that we offer as options to users who are creating a workload based on the namespace/project filter in the top nav.

As of v2.6.7, the UI will allow users to create a new namespace at the same time as they create a workload. However, the workload creation form does not expose the option to create the namespace in a project. We should figure out:

• In the workload creation form, should we allow users to select a project for a new namespace?
• If you have a single project selected in the top nav, and you create a new namespace, should it automatically be created in the selected project?
• How would we make it visually clear which project the new namespace would be created in?
• In the dropdown menu for selecting a namespace, should the namespaces be grouped by project?

This screenshot shows the current UX for creating a workload in a new namespace. If a project is selected in the top nav, should we prompt the user to select a project here as well?