[Nexthop] Bump cmd_config_test to size=large

The suite is ~60 files of ConfigSession-backed tests, each doing several
fsync-backed writeFileAtomic calls per case; with this PR's added
peer-group tests the full run takes ~530s on a dev box and timed out at
Bazel's default moderate limit (300s) in the bazel-build CI job — killed
mid-fsync in ConfigSessionTestFixture.commandTrackingMultipleCommands,
50/51 remaining tests green. size=large raises the test timeout to 900s
(same precedent as thrift_packet_stream/tests).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hillol-nexthop

fboss/cli/fboss2/test/config/BUCK

@@ -5,6 +5,10 @@ oncall("fboss_oss")
 
 cpp_unittest(
     name = "cmd_config_test",
+    # The suite is ~60 files of ConfigSession tests, each doing several
+    # fsync-backed writeFileAtomic calls; on CI disks the run can exceed the
+    # default "moderate" (300s) Bazel test timeout.
+    size = "large",
     srcs = [
         "BgpConfigSessionTest.cpp",
         "CmdConfigAclRuleTest.cpp",