[Serverless]: Create API Key UI states that No Expiration is a Default

### Serverless Docs

Elasticsearch

### Description

Go to the "Getting Started with Elasticsearch" homepage, then scroll down to the "Add an API Key" section. Click +New. The screen shown has "Apply expiration date" enabled, but the text immediately beneath it states "Setting an expiration date is a security best practice. **Defaults to no expiration.**"

This is contradictory as it defaulted to having an expiration.


### Resources and additional context

Found during the Serverless Bugbash but the issue is about the UI.