invoke SimpleHttpCommandCenter stop method, add earlier initialize gateway type

[oawang]

1. 修复 SimpleHttpCommandCenter 线程关闭问题
2. 增加SentinelConfigGatewayTypeInitializer 提前设置网关 APPType， 修复 SentinelSCGAutoConfiguration initAppType() 存在不生效问题

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✅ oawang
❌ qiujw

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