Update VPN setup instructions and add image

[CarlosLopezElorduy]

This pull request significantly updates the VPN setup documentation for IRB, focusing on a new, streamlined process using FortiClient. The instructions are now clearer and more step-by-step, with outdated details about two-factor authentication and previous Linux setup methods removed. The new version also adds guidance for terminal usage and includes helpful links and images.

Major documentation update and simplification:

• Rewrote the VPN setup instructions to focus on installing and configuring FortiClient, providing a clear step-by-step process with direct download links and visuals.
• Removed outdated sections related to two-factor authentication setup and the previous OpenConnect-based Linux instructions, consolidating the guide around the new FortiClient workflow.

Linux-specific improvements:

• Added specific terminal commands for Ubuntu users to configure DNS resolution for the VPN, replacing previous troubleshooting steps.
• Provided detailed instructions for importing the VPN configuration file and managing connections through both the FortiClient GUI and terminal commands.

[Copilot]

Pull request overview

This pull request updates the IRB VPN setup documentation by replacing the previous OpenConnect-based instructions with new FortiClient-based instructions. The changes remove outdated two-factor authentication setup details and Linux-specific OpenConnect troubleshooting, replacing them with streamlined FortiClient installation and configuration steps.

Changes:

• Replaced OpenConnect VPN setup instructions with FortiClient-based workflow
• Added FortiClient installation guide with download links and terminal commands for Ubuntu DNS configuration
• Included new screenshot image showing the FortiClient download page and added terminal command reference table

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated 9 comments.

File	Description
docs/IRB/VPN.md	Complete rewrite of VPN setup instructions, replacing OpenConnect with FortiClient installation and configuration steps
docs/assets/images/forticlient_web.png	New PNG image showing FortiClient download page (binary file)

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[CarlosLopezElorduy]

@copilot address the PR comments, and also lint the markdown

[Copilot]

@CarlosLopezElorduy I've opened a new pull request, #312, to work on those changes. Once the pull request is ready, I'll request review from you.