fix(ping): correct flag default and bind pflags to viper

[bosiakov]

What this PR does / Why we need it:

Fixes two bugs in cmd/ping/main.go's command-line flag handling:

1. The --udp-rate-limit flag was reading its default from httpResponseFlag (a string flag defaulting to "ok"). viper.GetFloat64("ok") returns 0, so the documented default of 20 never took effect — the actual default was 0.
2. parseEnvFlags called pflag.Parse() but never invoked viper.BindPFlags(pflag.CommandLine), so values passed on the command line (--http-response=..., --udp-rate-limit=...) were parsed and then silently dropped — only the viper defaults and the bound env vars surfaced in the resulting config.

The fix mirrors the pattern used by every other cmd/*/main.go (allocator, controller, extensions, processor, sdk-server), all of which call runtime.Must(viper.BindPFlags(pflag.CommandLine)) after their BindEnv calls.

[lacroixthomas]

Oh nice catch !

[lacroixthomas]

/gcbrun

[agones-bot]

Build Failed 😭

Build Id: b0f86c9f-3b60-42a4-88f4-80a3d5a110c7

Status: FAILURE

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[lacroixthomas]

/gcbrun

It's a flaky test, probably not related
Just to keep track of it:

Step #2 - "e2e-stable": VERBOSE: time="2026-04-30 00:15:04.616" level=info msg="GameServer Ready" gs=game-serversnvw2
Step #2 - "e2e-stable": VERBOSE:     gameserver_test.go:1055: 
Step #2 - "e2e-stable": VERBOSE:         	Error Trace:	/go/src/agones.dev/agones/test/e2e/gameserver_test.go:1055
Step #2 - "e2e-stable": VERBOSE:         	Error:      	Received unexpected error:
Step #2 - "e2e-stable": VERBOSE:         	            	dial tcp 34.74.214.65:7579: connect: connection refused
Step #2 - "e2e-stable": VERBOSE:         	Test:       	TestGameServerTcpProtocol
Step #2 - "e2e-stable": VERBOSE: --- FAIL: TestGameServerTcpProtocol (3.23s)

[agones-bot]

Build Failed 😭

Build Id: a99bfb73-7a8b-4dd6-b41e-3576f762e7ed

Status: FAILURE

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