[vybhav-nexthop]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

Summary

show config running only had an agent child, so fboss2-dev show config running bgp failed with A subcommand is required; BGP running config was only reachable as show bgp config running.

This makes show config running <daemon> the canonical form for running-config views:

• oss/CmdList.cpp: register bgp under show config running, reusing CmdShowConfigRunningBgp.
• show bgp config running is kept as an alias for backward compatibility; it was the only OSS spelling before this change.
• CmdShowConfigTraits.h: the description said the OSS build does not register show config running bgp; updated to name it as the primary spelling.
• CmdHandler.cpp: fix --fmt json for commands whose RetType is folly::dynamic (show config running bgp|agent, show bgp config running, show bgp policy). printJson passed the per-host map to SimpleJSONSerializer, which threw TypeError: expected dynamic type 'array', but had type 'object' and exited 1. It now renders folly::dynamic results with folly::toJson.
• docs/docs/debugging/fboss_cli.md: command table lists show config running agent / bgp.

Test Plan

On a hardware switch running bgpd:

Command	Before	After
show config running bgp	A subcommand is required, rc=106	BGP running-config JSON, rc=0
show bgp config running	JSON, rc=0	same, rc=0
show config running agent	rc=0	identical output, rc=0

show config running bgp output is byte-identical to show bgp config running. show config running --help lists agent and bgp.

--fmt json fix (CmdHandler.cpp): before / after

On a hardware switch, bgpd running. Before = the installed fboss2-dev; after = this PR's build.

Command	Before	After
--fmt json show bgp config running	rc=1, TypeError: expected dynamic type 'array', but had type 'object'	rc=0, valid JSON {"localhost": {...}} (861,551 bytes)
--fmt json show config running bgp	rc=106, A subcommand is required	rc=0, byte-identical (cmp) to the row above
--fmt json show bgp policy (no policy name)	usage message, then rc=1 TypeError: ...	usage message, rc=0, {"localhost":{}}

Start of the after output:

{"localhost":{"defaultCommandLineArgs":{"publish_stats_to_fsdb":"true","publish_state_to_fsdb":"true",...},"local_confed_as_4_byte":...

--fmt json show config running agent was not re-checked in this run: the agent on that switch was not configured (switch is still initializing or is exiting and is not fully configured yet) with both binaries. It is covered by ShowConfigRunningAgentTest.JsonMatchesDaemonRunningConfig.

New integration tests in fboss2_integration_test, all passing (3/3) on a hardware switch with a BGP peer established:

• ShowConfigRunningAgentTest.JsonMatchesDaemonRunningConfig: show config running agent matches the agent's getRunningConfig RPC.
• ShowConfigRunningBgpTest.MatchesDaemonRunningConfig: show config running bgp matches bgpd's getRunningConfig RPC.
• ShowConfigRunningBgpTest.MatchesShowBgpConfigRunningAlias: show config running bgp matches show bgp config running.