add VpnDetails enum to VpnConnectionInfo

[cachebag]

part of #288.

changes

add protocol-specific detail reporting when calling get_vpn_info:

#[non_exhaustive]
pub enum VpnDetails {
    WireGuard {
        public_key: Option<String>,
        endpoint: Option<String>,
    },
    OpenVpn {
        remote: String,
        port: u16,
        protocol: String,
        cipher: Option<String>,
        auth: Option<String>,
        compression: Option<String>,
    },
}

add pub details: Option<VpnDetails> to VpnConnectionInfo (non-breaking, struct is #[non_exhaustive]).

populate from vpn.data dict for openvpn, from wireguard section properties for wireguard.