force eml file to be parsed by EMAIL (#2615)

### What problem does this PR solve?
#2613
### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/dataset_api.py

                 doc["parser_id"] = ParserType.AUDIO.value
             if re.search(r"\.(ppt|pptx|pages)$", filename):
                 doc["parser_id"] = ParserType.PRESENTATION.value
+            if re.search(r"\.(eml)$", filename):
+                doc["parser_id"] = ParserType.EMAIL.value
             DocumentService.insert(doc)
 
             FileService.add_file_from_kb(doc, kb_folder["id"], dataset.tenant_id)

api/apps/document_app.py

             doc["parser_id"] = ParserType.AUDIO.value
         if re.search(r"\.(ppt|pptx|pages)$", filename):
             doc["parser_id"] = ParserType.PRESENTATION.value
+        if re.search(r"\.(eml)$", filename):
+            doc["parser_id"] = ParserType.EMAIL.value
         DocumentService.insert(doc)
         FileService.add_file_from_kb(doc, kb_folder["id"], kb.tenant_id)
     except Exception as e: