Add hooks overrides support with environment variables

- Added WG_PRE_UP, WG_POST_UP, WG_PRE_DOWN, WG_POST_DOWN environment variables
- Created applyHooksOverrides() helper function
- Updated WireGuard service to apply hooks overrides when generating config
- Updated /api/admin/overrides endpoint to include hooks override information
- Updated documentation with hooks environment variables

Co-authored-by: kaaax0815 <32197462+kaaax0815@users.noreply.github.com>

src/server/utils/WireGuard.ts

@@ -27,10 +27,11 @@ class WireGuard {
   async #saveWireguardConfig(wgInterface: InterfaceType) {
     const clients = await Database.clients.getAll();
     const hooks = await Database.hooks.get();
+    const hooksWithOverrides = applyHooksOverrides(hooks);
 
     const result = [];
     result.push(
-      wg.generateServerInterface(wgInterface, hooks, {
+      wg.generateServerInterface(wgInterface, hooksWithOverrides, {
         enableIpv6: !WG_ENV.DISABLE_IPV6,
       })
     );