feat(server): increase embedding jobs concurrency & handle empty content after trim (#12574)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **Improvements**
  - Increased the default concurrency for background tasks, enhancing processing efficiency.
  - Improved handling of empty or unsupported documents to ensure consistent processing.
  - Optimized document filtering to exclude certain documents from processing, improving performance.

- **Bug Fixes**
  - Enhanced detection of empty document summaries, reducing errors during processing.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.docker/selfhost/schema.json

@@ -52,14 +52,14 @@
         },
         "queues.copilot": {
           "type": "object",
-          "description": "The config for copilot job queue\n@default {\"concurrency\":5}",
+          "description": "The config for copilot job queue\n@default {\"concurrency\":10}",
           "properties": {
             "concurrency": {
               "type": "number"
             }
           },
           "default": {
-            "concurrency": 5
+            "concurrency": 10
           }
         },
         "queues.doc": {