Use relative URL for swagger.json to support reverse proxy deployments

[EkberHasanov]

Problem

When Node-RED is deployed behind a reverse proxy with a subpath (e.g., /<NODERED-URL>/), the Swagger UI fails to load the OpenAPI specification because it uses a hardcoded absolute path.

Current behavior:

• Swagger UI is accessed at: /<NODERED-URL>/swagger-ui/swagger-ui.html
• It requests: /http-api/swagger.json (absolute path)
• This results in a 404 error because the endpoint is actually at /<NODERED-URL>/http-api/swagger.json

Solution

Change the swagger.json URL from absolute to relative path:

- url: "/http-api/swagger.json",
+ url: "../http-api/swagger.json",

Why this works

- Without proxy: Resolves to /http-api/swagger.json ✓
- Behind proxy: Resolves to /nodered-server/http-api/swagger.json ✓

This is a non-breaking change that makes the library compatible with standard reverse proxy deployments (nginx, Apache, etc.) while maintaining existing functionality.

Testing

Tested with Node-RED behind Apache reverse proxy with ProxyPass /<NODERED-URL>/ http://nodered:1880/

I did something like this which resolves the issue:
@digital-tvilling+node-red-openapi-generator+1.1.1.patch - file:

diff --git a/node_modules/@digital-tvilling/node-red-openapi-generator/swagger/swagger-ui/swagger-ui.html b/node_modules/@digital-tvilling/node-red-openapi-generator/swagger/swagger-ui/swagger-ui.html
index 1f10733..69d6654 100644
--- a/node_modules/@digital-tvilling/node-red-openapi-generator/swagger/swagger-ui/swagger-ui.html
+++ b/node_modules/@digital-tvilling/node-red-openapi-generator/swagger/swagger-ui/swagger-ui.html
@@ -13,7 +13,7 @@
   <script>
   window.onload = function() {
     const ui = SwaggerUIBundle({
-      url: "/http-api/swagger.json", 
+      url: "../http-api/swagger.json", 
       dom_id: '#swagger-ui',
       deepLinking: true,
       presets: [

[EkberHasanov]

@johanhanses what do you think? I can raise a PR too