Update Xubuntu installation guide for latest VirtualBox version

[amishaaa129]

Because

The installation process for Xubuntu in VirtualBox has changed in the newer version of VirtualBox. The current guide on The Odin Project’s Foundations path does not reflect these updates, which can cause confusion for new students following the setup instructions.

This PR

• Updated the Xubuntu installation guide to match the new VirtualBox interface and setup process.
• Changed references from “pages” to “dropdowns” where applicable, as setup screens now use collapsible dropdown menus.
• Modified instructions regarding the “Proceed with unattended installation” checkbox, which is now ticked by default.
• Updated video memory settings to reflect the new default (16 MB) and added instructions to manually increase it to 128 MB for proper display scaling.
• Added troubleshooting and configuration steps for Chrome connectivity issues in Xubuntu due to default NAT settings, with instructions to switch to a Bridged Adapter.

Issue

Closes #30173

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Foundations: Update Xubuntu installation guide
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide