[Website]: Manage budgets and notifications

### Before you submit

- [x] This issue is about a documentation page, flow, or piece of content.

### Type of issue

Missing information

### What documentation page or section is affected

https://www.elastic.co/docs/deploy-manage/cloud-organization/billing/manage-billing-notifications

### What happened?

This document is missing an explanation of whether the deployment and billing can exceed the budget? Is the budget a hard limit?
Add an explanation something like this:
"The billing budget on Elastic Cloud (ESS/ECH) is a notification threshold only, it is not a hard cap. When your month-to-date usage reaches the configured notification threshold, (e.g, 70% or 100% of the configured budget), Elastic sends email alert notifications, but your deployment continues to run uninterrupted and usage can exceed the budget. There is no hard stop of the deployment when the budget limit is hit."

### Additional info

_No response_

Start with the affected Manage billing notifications page linked in the issue and review the budget section. Add the requested explanation that budgets trigger email notifications but do not stop deployments or cap usage, then verify the documentation preview and wording.

Written by the indexing model from the issue text.