refactor: remove /api/config endpoint - now served by nginx

- Delete api/controllers/config.js (unused by frontends)
- Remove /config route from swagger.yaml
- Delete docs/ENVIRONMENT_CONFIGURATION.md (outdated)
- Clean up Helm env vars: remove debugMode, API_PUBLIC_PATH, ENVIRONMENT, BANNER_COLOUR, ANALYTICS_* from values files

Config now served by nginx from rproxy-config ConfigMap.
eagle-api only needs internal env vars (MongoDB, Minio, CHES, ClamAV).

Author: danieltruong

api/controllers/config.js

@@ -691,10 +691,6 @@ definitions:
       message:
         type: string
 
-  ### Config Definitions
-  ConfigObject:
-    type: object
-
 ### Task Definitions
   TaskObject:
     type: object
@@ -718,38 +714,6 @@ definitions:
           - default
 ### Path Definitions
 paths:
-  /config:
-    x-swagger-router-controller: config
-    options:
-      tags:
-        - config
-      summary: 'Pre-flight request'
-      operationId: protectedOptions
-      description: 'Options on config Route'
-      responses:
-        '200':
-          description: 'Success'
-          schema:
-            $ref: '#/definitions/ConfigObject'
-        '403':
-          description: 'Access Denied'
-          schema:
-            $ref: '#/definitions/Error'
-    get:
-      tags:
-        - config
-      summary: 'Get the app configuration'
-      operationId: publicGetConfig
-      description: 'Retrieves configuration data.'
-      responses:
-        '200':
-          description: 'Success'
-          schema:
-            $ref: '#/definitions/ConfigObject'
-        '403':
-          description: 'Access Denied'
-          schema:
-            $ref: '#/definitions/Error'
   /login/token:
     x-swagger-router-controller: login
     options: