refactor: expose flow batching mode constants to config (#6442)

* refactor: make flow batching mode constant to configs

Signed-off-by: discord9 <discord9@163.com>

* docs: config docs

Signed-off-by: discord9 <discord9@163.com>

* docs: update code comment

Signed-off-by: discord9 <discord9@163.com>

* test: fix test_config_api

Signed-off-by: discord9 <discord9@163.com>

* feat: more batch opts

Signed-off-by: discord9 <discord9@163.com>

* fix after rebase

Signed-off-by: discord9 <discord9@163.com>

* chore: per review

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* per review experimental options

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Signed-off-by: discord9 <discord9@163.com>

config/flownode.example.toml

@@ -7,6 +7,29 @@ node_id = 14
 ## The number of flow worker in flownode.
 ## Not setting(or set to 0) this value will use the number of CPU cores divided by 2.
 #+num_workers=0
+[flow.batching_mode]
+## The default batching engine query timeout is 10 minutes.
+#+query_timeout="600s"
+## will output a warn log for any query that runs for more that this threshold
+#+slow_query_threshold="60s"
+## The minimum duration between two queries execution by batching mode task
+#+experimental_min_refresh_duration="5s"
+## The gRPC connection timeout
+#+grpc_conn_timeout="5s"
+## The gRPC max retry number
+#+experimental_grpc_max_retries=3
+## Flow wait for available frontend timeout,
+## if failed to find available frontend after frontend_scan_timeout elapsed, return error
+## which prevent flownode from starting
+#+experimental_frontend_scan_timeout="30s"
+## Frontend activity timeout
+## if frontend is down(not sending heartbeat) for more than frontend_activity_timeout,
+## it will be removed from the list that flownode use to connect
+#+experimental_frontend_activity_timeout="60s"
+## Maximum number of filters allowed in a single query
+#+experimental_max_filter_num_per_query=20
+## Time window merge distance
+#+experimental_time_window_merge_threshold=3
 
 ## The gRPC server options.
 [grpc]