Fixes error in Articulation where default_joint_stiffness and default_joint_damping is not correctly set if actuator is instance of ImplicitActuator (#1580)

# Description

Before the fix, the field, default_joint_stiffness, and
default_joint_damping in omni.isaac.lab.assets.Articulation will be
the default value configured Joint Drive property in usd file, and
defining a new value with actuator config will not have effect
if the actuator is type ImplicitActuator

after the fix, all actuator types will be able to override
default_joint_stiffness and default_joint_damping

Fixes #1552 

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## Type of change

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

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## Checklist

- [X] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] 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
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---------
Signed-off-by: Kelly Guo <kellyguo123@hotmail.com>
Co-authored-by: Kelly Guo <kellyguo123@hotmail.com>
Co-authored-by: James Tigue <166445701+jtigue-bdai@users.noreply.github.com>
Co-authored-by: Kelly Guo <kellyg@nvidia.com>