[k8s] Install ray dashboard dependencies in CPU k8s image

[romilbhardwaj]

Fresh builds of our k8s CPU image would fail during provisioning with:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/sky/.local/lib/python3.10/site-packages/sky/skylet/ray_patches/__init__.py", line 85, in patch
    from ray.dashboard.modules.job import job_head
  File "/home/sky/.local/lib/python3.10/site-packages/ray/dashboard/modules/job/job_head.py", line 9, in <module>
    import aiohttp.web
ModuleNotFoundError: No module named 'aiohttp'

This is because ray dashboard dependencies are not correct installed.

This PR changes ray installation in our Dockerfile to also install dashboard dependencies.

GPU image does not need this change since the base image installs ray[default] anyway.

cc @kbrgl

[Michaelvll]

LGTM! Thanks @romilbhardwaj!