fix: hide Expose Port option for Nebius instances with fixed ports label

[hakhandelwal11]

• Nebius instances with the fixed Ports label were displaying the Expose Port option during export.
• Nebius instances included the Modify Firewall capability, causing them to pass the canModifyFirewallCapability check on the UI and making the Expose Port option accessible.
• This change updates the Nebius instance configuration to exclude the Modify Firewall capability. The UI now returns the appropriate error message when attempting to expose ports for Nebius instances.