Update aws.md to clarify containers can be billable

[jhjacobson]

Clarifying that containers can be billable per customer's feedback

What does this PR do? What is the motivation?

a customer pointed out that containers can actually be billable as documented here. They asked if we could clarify that this is the case given that we call out custom metrics as billable.

Merge instructions

I'm not sure if this will be more confusing since it isn't always the case that it's billable. But containers have an allotment similar to custom metrics so it seems fair to call it out here.
Merge readiness:

• Ready for merge

Merge queue is enabled in this repo. To have it automatically merged after it receives the required reviews, create the PR (from a branch that follows the <yourname>/description naming convention) and then add the following PR comment:

/merge

Additional notes

[maycmlee]

/merge

[dd-devflow]

View all feedbacks in Devflow UI.
2025-02-25 18:41:56 UTC ℹ️ Start processing command /merge

---

2025-02-25 18:42:02 UTC ℹ️ MergeQueue: waiting for PR to be ready

This merge request is not mergeable yet, because of pending checks/missing approvals. It will be added to the queue as soon as checks pass and/or get approvals.
Note: if you pushed new commits since the last approval, you may need additional approval.
You can remove it from the waiting list with /remove command.

---

2025-02-25 22:43:05 UTC ⚠️ MergeQueue: This merge request was unqueued

devflow unqueued this merge request: It did not become mergeable within the expected time

[maycmlee]

Thanks @jhjacobson for opening this PR! I opened a new PR with the correct branch naming format (<your_name>/<branch_name>): #28116, so will close this one.