Feat: pipeline supports PPTX (#10167)

### What problem does this PR solve?

Pipeline supports parsing PPTX naively (text only).

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

rag/flow/tests/dsl_examples/general_pdf_all.json

@@ -38,6 +38,13 @@
                   ],
                   "output_format": "json"
                 },
+                "slides": {
+                    "parse_method": "presentation",
+                    "suffix": [
+                        "pptx"
+                    ],
+                    "output_format": "json"
+                },
                 "markdown": {
                   "suffix": [
                     "md",