[Feature Request] Add "Edit routes" button to Client Certificates for per-user CCD configuration

[Shkarlatov]

Overview:

Add a simple, focused interface to manage per-user CCD (Client Config Directory) configurations directly from the existing Client Certificates tab. This provides administrators with quick access to configure static IPs, routes, and other client-specific settings without leaving the certificate management context. Similar in the project https://github.com/palark/ovpn-admin

Current Limitation:

Currently, to configure per-client settings (static IPs, custom routes via CCD files), administrators must manually create/edit files in the OpenVPN server's CCD directory via SSH. There's no UI integration for this essential functionality in OpenVPN-UI.

Proposed Solution:

Add an "Edit routes" action button in the Client Certificates table that opens a modal dialog for configuring CCD settings specific to that user/certificate.