streams: update the config section name

Summary:
The commit-fetch-batch-size is not specific to agent detection, this diff moves
it to experimental config section

Reviewed By: genevievehelsel

Differential Revision: D99291462

fbshipit-source-id: 54fecfa789fb4e5f1993f29c2a0458673808bf7f

Author: zzl0

eden/scm/sapling/streams.py

@@ -26,7 +26,7 @@ def prefetchtextstream(
 def _prefetchtextstream(repo, ctxstream):
     is_agent = agentdetect.is_agent()
     max_count = repo.ui.configint("agent", "max-commit-fetch-count", 100_000)
-    batch_size = repo.ui.configint("agent", "commit-fetch-batch-size", 10_000)
+    batch_size = repo.ui.configint("experimental", "commit-fetch-batch-size", 10_000)
     count = 0
 
     for ctxbatch in util.eachslice(ctxstream, batch_size, maxtime=2):

eden/scm/tests/test-agent-perf-detection.t

@@ -1,6 +1,6 @@
   $ enable rebase
   $ setconfig agent.max-commit-fetch-count=6
-  $ setconfig agent.commit-fetch-batch-size=2
+  $ setconfig experimental.commit-fetch-batch-size=2
   $ export CODING_AGENT_METADATA=id=test_agent
 
 Repo setup