[k8s] Surface docker permission error for sky local up

[Shrinandan-N]

Fixes #2592.

This pull request updates create_cluster.sh to enhance the handling of Docker permission errors. The revised script captures the output and error messages from docker info. It identifies and distinguishes between 'permission denied' errors and scenarios where Docker is not running, and alerts the user with an error message accordingly.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Created test user without docker permission (not in docker group) and verified that a permission error was reported instead of the standard "Docker is not running" error.
• Added test user to docker group and ran sky local up to ensure that permission error/docker error did not prevail after docker permissions were granted.

[romilbhardwaj]

Awesome, thanks @Shrinandan-N! Left a minor comment, otherwise good to go!

[Shrinandan-N]

Sounds good @romilbhardwaj, accepted the commit suggestion!