[feature request] add metric to track sandbox creation latency and success rate

[furykerry]

What would you like to be added:

Currently, we have no metric that measures the quality of sandbox creation. I propose to add several custom metrics that will measure the following:

1. sandbox_creation_latency_ms : "What was the total time from the moment a user request the sandbox creation to the moment the sandbox manager returns"
2. sandbox_creation_responses: "How many sandbox creations requests? and among them, how many are failures"

Why is this needed:

[DCchoudhury15]

/assign

[DCchoudhury15]

Hi @furykerry,
I noticed that the E2E-1.32 tests are currently failing with an InplaceUpdating error:
"inplace update is incompleted" ... "Pod is in deleting, and wait a moment"

While I have implemented the metrics for #60 strictly within the sandbox-manager's ClaimSandbox logic, I want to ensure I haven't introduced any unintended side effects. I observed that other recent PRs (e.g., #64) are encountering similar failures, which might suggest an upstream environment flake.

However, to ensure the highest quality for this PR, could you please guide me on the following:

1. Is there any architectural path where the Manager's claiming/locking latency could trigger a timeout in the Controller's InplaceUpdate logic?
2. Are there specific logs or debug steps you recommend to confirm that the metrics.go registration isn't interfering with the Kind cluster's stability in CI?

I have verified that all local unit tests pass and the project builds successfully. I am eager to learn more about the interaction between these components and am happy to adjust the implementation based on your feedback!

[DCchoudhury15]

I have merged the latest upstream/master into this branch, and all checks, including the E2E-1.32 / sandbox tests, are now passing successfully. This confirms that the previous failures were transient environment flakes and not related to the metrics instrumentation.

The PR is now fully verified and ready for final review. CC @furykerry