Add e2e test for `SandboxWarmPool` template updates

[janetkuo]

To ensure the robustness and predictability of SandboxWarmPool, it is important to have an e2e test that validates its behavior when the underlying sandbox template is updated. This is a critical scenario for seamless rollouts and to guarantee that the warm pool provides sandboxes with the correct and most up-to-date configuration.

This test would prevent potential regressions and provide confidence in the update process of SandboxWarmPool.

Scenario to test

1. A SandboxWarmPool is created with an initial template.
2. The template backing the SandboxWarmPool is updated to a new version.
3. A new SandboxClaim is created to request a sandbox from the pool.

Acceptance Criteria

• The test verifies that the SandboxClaim is fulfilled with a sandbox that is running the new version of the template.
• The test should also ideally verify that the existing pods in the warm pool are eventually replaced with pods running the new template version.