chore: expose add_flow_def() as an API under cocoindex module (#719)

Author: georgeh0

docs/docs/core/flow_def.mdx

@@ -40,7 +40,7 @@ def demo_flow_def(flow_builder: cocoindex.FlowBuilder, data_scope: cocoindex.Dat
     ...
 
 # Add the flow definition to the flow registry.
-demo_flow = cocoindex.flow.add_flow_def("DemoFlow", demo_flow_def)
+demo_flow = cocoindex.add_flow_def("DemoFlow", demo_flow_def)
 ```
 
 In both cases, `demo_flow` will be an object with `cocoindex.Flow` class type.

python/cocoindex/__init__.py

@@ -11,6 +11,7 @@
 from .flow import flow_def
 from .flow import EvaluateAndDumpOptions, GeneratedField
 from .flow import FlowLiveUpdater, FlowLiveUpdaterOptions
+from .flow import add_flow_def
 from .flow import update_all_flows_async, setup_all_flows, drop_all_flows
 from .lib import init, start_server, stop
 from .llm import LlmSpec, LlmApiType
@@ -52,6 +53,7 @@
     "GeneratedField",
     "FlowLiveUpdater",
     "FlowLiveUpdaterOptions",
+    "add_flow_def",
     "update_all_flows_async",
     "setup_all_flows",
     "drop_all_flows",