vmap support for linalg.lu_factor (#94328)
Differential Revision: D43093457
Fix #91415
### Expected behaviour
No use warning.
```python
from functorch import vmap
x = torch.randn(4, 3, 2)
z = vmap(torch.linalg.lu_factor)(x)
```
Same behaviour as for-loop:
```python
x = torch.randn(4, 3, 2)
results = []
for xi in x:
y = torch.linalg.lu_factor(xi)
results.append(y)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94328
Approved by: https://github.com/zou3519, https://github.com/Skylion007, https://github.com/Chillee
