feat: run the Podman driver as a launched external driver by default #5390

Part of #5200.

User Story

As an OpenShell Maintainer I want the desktop drivers to exist in their own repository so that their ownership and maintenance can be considered separately to core OpenShell. Podman has to run as a separate process first.

Problem Statement

Same as Docker (see #5389), for openshell-driver-podman. The additional-CA e2e (podman-additional-ca-e2e) refuses to run with an external driver.

Impact / Why This Matters

Same as Docker.

Proposed Design

Same as Docker. Podman's standalone --sandbox-additional-ca-bundle flag is out of scope. It is the only way an operator-managed external Podman driver gets a private CA, because the gateway rejects network trust for endpoint-override drivers. Revisit once launched and operator-managed drivers receive gateway trust.

Acceptance Criteria

• Existing Podman e2e suites pass on the external path.
• podman-additional-ca-e2e passes against the launched driver, and the wrapper script's "in-process only" guard is removed.
• Create and streaming latency are recorded against the linked path.
• Driver names, auto-detect order, and config tables work as before.

Alternatives Considered

• Same as Docker.