Hide Indexsets API in cloud API browser

[patrickmann]

/nocl under the hood change Resolves Graylog2/graylog-plugin-enterprise#8798

Description

Hide this API in swagger and the UI API browser, when in Cloud environment.

Motivation and Context

See linked issue

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Refactoring (non-breaking change)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] 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 read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.