Disables default viewport when headless but cameras are enabled

[kellyguo11]

Description

When cameras are enabled, a default render product always gets created for the viewport, which brings additional overhead for rendering the viewport at each step. However, when running in headless mode, we may not need to render the viewport if we are not recording or livestreaming.

This change disables viewport rendering in the headless cases where recording and livestreaming are not required.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[Mayankm96]

Renamed the title to make it clear which scenarios are being referred to.

Also adding @hhansen-bdai as a reviewer to check as well.