Set saas endpoint as global to skip region checks

[claudia-correia]

Description

Updates the list of global APIs to include the /saas endpoint.

Related Issues

https://elasticco.atlassian.net/browse/CP-7863

Motivation and Context

The /saas/billing/prices endpoint is a global endpoint that doesn't require the /regions/$region prefix. However, if this endpoint isn't added to the global list, trying to use it in the cloud-cli code without specifying a region in the context will result in this error the requested operation requires a region but none has been set.

How Has This Been Tested?

Tested using the new cloud-cli changes from https://github.com/elastic/cloud-cli/pull/1525, which perform a GET /saas/billing/prices request.

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