feat: supported langflow api provider (#1646)

* add langflow api provider

* chore: migration

* feat: okay for non-stream req

* fix: langflow sse data extracting

* doc: add comment on langflow api

---------

Co-authored-by: Junyan Qin <rockchinq@gmail.com>

pkg/persistence/migrations/dbm006_langflow_api_config.py

@@ -0,0 +1,45 @@
+from .. import migration
+
+import sqlalchemy
+
+from ...entity.persistence import pipeline as persistence_pipeline
+
+
+@migration.migration_class(6)
+class DBMigrateLangflowApiConfig(migration.DBMigration):
+    """Langflow API config"""
+
+    async def upgrade(self):
+        """Upgrade"""
+        # read all pipelines
+        pipelines = await self.ap.persistence_mgr.execute_async(sqlalchemy.select(persistence_pipeline.LegacyPipeline))
+
+        for pipeline in pipelines:
+            serialized_pipeline = self.ap.persistence_mgr.serialize_model(persistence_pipeline.LegacyPipeline, pipeline)
+
+            config = serialized_pipeline['config']
+
+            if 'langflow-api' not in config['ai']:
+                config['ai']['langflow-api'] = {
+                    'base-url': 'http://localhost:7860',
+                    'api-key': 'your-api-key',
+                    'flow-id': 'your-flow-id',
+                    'input-type': 'chat',
+                    'output-type': 'chat',
+                    'tweaks': '{}',
+                }
+
+            await self.ap.persistence_mgr.execute_async(
+                sqlalchemy.update(persistence_pipeline.LegacyPipeline)
+                .where(persistence_pipeline.LegacyPipeline.uuid == serialized_pipeline['uuid'])
+                .values(
+                    {
+                        'config': config,
+                        'for_version': self.ap.ver_mgr.get_current_version(),
+                    }
+                )
+            )
+
+    async def downgrade(self):
+        """Downgrade"""
+        pass