openvpn: move legacy implementation into a plugin

[fichtner]

Important notices

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• I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
• I am convinced that my issue is new after having checked both open and closed issues at https://github.com/opnsense/core/issues?q=is%3Aissue

Is your feature request related to a problem? Please describe.

OpenVPN client/server GUI has been deprecated for a while.

Describe the solution you like

To keep the code and user base we will move it to a plugin. os-openvpn-legacy is probably fitting leaving the door open for os-openvpn.

The OpenVPN server wizard will not be part of the plugin as the wizard is also going to be replaced in 25.7.

Describe alternatives you considered

Removing the code.

Additional context

N/A

[fichtner]

Same here, remove some util.inc cruft:

% git grep '[^_]get_[^i]' src/www/vpn_openvpn_*
src/www/vpn_openvpn_client.php:              $interfaces = get_configured_interface_with_descr();
src/www/vpn_openvpn_client.php:              $carplist = get_configured_carp_interface_list();
src/www/vpn_openvpn_client.php:                  $interfaces[$cif.'|'.$carpip] = $carpip." (".get_vip_descr($carpip).")";
src/www/vpn_openvpn_client.php:              $aliaslist = get_configured_ip_aliases_list();
src/www/vpn_openvpn_client.php:                  $interfaces[$aliasif.'|'.$aliasip] = $aliasip." (".get_vip_descr($aliasip).")";
src/www/vpn_openvpn_server.php:                        $interfaces = get_configured_interface_with_descr();
src/www/vpn_openvpn_server.php:                        foreach (get_configured_carp_interface_list() as $cif => $carpip) {
src/www/vpn_openvpn_server.php:                            $interfaces[$cif.'|'.$carpip] = $carpip." (".get_vip_descr($carpip).")";
src/www/vpn_openvpn_server.php:                        foreach (get_configured_ip_aliases_list() as $aliasip => $aliasif) {
src/www/vpn_openvpn_server.php:                            $interfaces[$aliasif.'|'.$aliasip] = $aliasip." (".get_vip_descr($aliasip).")";
src/www/vpn_openvpn_server.php:                        $serverbridge_interface = array_merge($serverbridge_interface, get_configured_interface_with_descr());
src/www/vpn_openvpn_server.php:                        foreach (get_configured_carp_interface_list() as $cif => $carpip) {
src/www/vpn_openvpn_server.php:                            $serverbridge_interface[$cif.'|'.$carpip] = $carpip." (".get_vip_descr($carpip).")";
src/www/vpn_openvpn_server.php:                        foreach (get_configured_ip_aliases_list() as $aliasip => $aliasif) {
src/www/vpn_openvpn_server.php:                            $serverbridge_interface[$aliasif.'|'.$aliasip] = $aliasip." (".get_vip_descr($aliasip).")";

[fichtner]

Migration in bc95a0f