[Onprem] Align Python Versions

[michaelzhiluo]

After some discussion, the conclusion from last week to align user and admin's python (for submitting Ray jobs, since the Ray cluster is launched via admin's python) is to add an admin_python field to the cluster config, indicating the path of admin's python binary.

cluster:
  ips:
  - 20.232.111.246
  name: azure-onprem

auth:
  ssh_user: test
  ssh_private_key: ~/.ssh/sky-key

admin_python: /usr/bin/python3

[concretevitamin]

Quick vote on naming?

• root_python
• runtime_python
• global_python
• python
• python_executable

I feel these are preferable to admin_python as a regular user should not need know about the "admin" deployment concept. Personally leaning towards the last two.