[Chore]: Update the URL fragment for API keys

[shasts]

Description

The API keys URL fragment was updated. But the docs here and a couple of other lingering pieces were not. This PR updates the reference in this repo to reflect the latest URL.

Corresponding cloud PR. https://github.com/elastic/cloud/pull/129503

Related Issues

Motivation and Context

How Has This Been Tested?

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (improves code quality but has no user-facing effect)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation

Readiness Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

[dimuon]

LGTM