Follow-up from "Remove namespace selector"

The following discussion from !13515 should be addressed:

• @vvempati started a discussion: (+2 comments)

  question: Do we need to pass this as an array now that we don't support namespace selection on SaaS purchase flow? Can we instead just send current_namespace here and update the frontend logic accordingly so we don't need to access the first item in the array to get the selected group in the following blocks:

  initializeSelectedGroup() {
        const [selectedGroup] = this.groups || [];
        ...
  }

  groups() {
        return (
          // Return the single pre-selected namespace
          this.namespaces ?? []
        );
      },

    current_namespace: @current_namespace.to_json,