Clarify elastic-cloud-api-keys doc (#4099)

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## Summary

ECH API key will disappear automatically once it's expired. It caused
confusion in [an internal ticket
here](elastic/sdh-control-plane#11238 (comment))
and this doc PR is to clarify that.


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## Preview before PR merge


[deploy-manage/api-keys/elastic-cloud-api-keys.md](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4099/deploy-manage/api-keys/elastic-cloud-api-keys)

## View after PR merge


https://www.elastic.co/docs/deploy-manage/api-keys/elastic-cloud-api-keys

Author: kunisen

deploy-manage/api-keys/elastic-cloud-api-keys.md

@@ -34,9 +34,11 @@ These keys provides access to the API that enables you to manage your deployment
 
     ::::{note}
     When an API key is nearing expiration, Elastic sends an email to the creator of the API key and each of the operational contacts. When you use an API key to authenticate, the API response header `X-Elastic-Api-Key-Expiration` indicates the key’s expiration date. You can log this value to detect API keys that are nearing expiration.
+
+    Once an API key expires, it will automatically be removed from the API Keys tab.
     ::::
 
-5. Click **Create API key**, copy the generated API key, and store it in a safe place. You can also download the key as a CSV file.
+6. Click **Create API key**, copy the generated API key, and store it in a safe place. You can also download the key as a CSV file.
 
 The API key needs to be supplied in the `Authorization` header of a request, in the following format: