[sc-150886] change default disk size to 200 gb

[amandineslx]

After discussion with Mickael, it has been decided to:

• keep field optional
• set min value to 0
• add documentation about the 0 meaning 200
• add comment in code and JSON about the default being used twice

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #150866: [EKS] Update the default EKS disk size.