Updates stack instance randomization default environments (#2251)

# Description

The instance randomization stack environments have multiple cameras in
the scene, which requires heavy resources on large numbers of
environments. This PR reduces the default environment so that they can
be run with less memory resources.


## Type of change

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applicable. -->

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

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] 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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source/isaaclab_tasks/isaaclab_tasks/manager_based/manipulation/stack/config/franka/stack_ik_rel_instance_randomize_env_cfg.py

@@ -27,6 +27,9 @@ class FrankaCubeStackInstanceRandomizeEnvCfg(
         # We switch here to a stiffer PD controller for IK tracking to be better.
         self.scene.robot = FRANKA_PANDA_HIGH_PD_CFG.replace(prim_path="{ENV_REGEX_NS}/Robot")
 
+        # Reduce the number of environments due to camera resources
+        self.scene.num_envs = 2
+
         # Set actions for the specific robot type (franka)
         self.actions.arm_action = DifferentialInverseKinematicsActionCfg(
             asset_name="robot",

source/isaaclab_tasks/isaaclab_tasks/manager_based/manipulation/stack/config/franka/stack_joint_pos_instance_randomize_env_cfg.py

@@ -75,6 +75,9 @@ class FrankaCubeStackInstanceRandomizeEnvCfg(StackInstanceRandomizeEnvCfg):
         # Set Franka as robot
         self.scene.robot = FRANKA_PANDA_CFG.replace(prim_path="{ENV_REGEX_NS}/Robot")
 
+        # Reduce the number of environments due to camera resources
+        self.scene.num_envs = 2
+
         # Set actions for the specific robot type (franka)
         self.actions.arm_action = mdp.JointPositionActionCfg(
             asset_name="robot", joint_names=["panda_joint.*"], scale=0.5, use_default_offset=True