Optimizes headless non-rendering app by using minimal fabric population (#504)

# Description

When running headless, with no cameras enabled, optimize init time by
only doing minimal fabric population, by turning off FSD.

## Type of change

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applicable. -->

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [ ] I have run the [`pre-commit` checks](https://pre-commit.com/) 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

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---------
Co-authored-by: Kelly Guo <kellyg@nvidia.com>

apps/isaaclab.python.headless.kit

@@ -74,9 +74,10 @@ app.hydraEngine.waitIdle = false
 omni.replicator.asyncRendering = false
 
 ### FSD
-app.useFabricSceneDelegate = true
-# Temporary, should be enabled by default in Kit soon
-rtx.hydra.readTransformsFromFabricInRenderDelegate = true
+# this .kit file is used for headless, no-rendering cases. There won't be a scene delegate
+# created, but setting useFSD to false here is done to not do full fabric population, but
+# instead to minimal population
+app.useFabricSceneDelegate = false
 
 # Enable Iray and pxr by setting this to "rtx,iray,pxr"
 renderer.enabled = "rtx"