chore: unify platform logging setup

[laotoutou]

Summary

• add shared observability.NewLogger for the platform zap JSON format and service field
• add observability.NewMigrateLogger and remove duplicated migration logger adapters
• refactor platform service entrypoints to use the shared logger setup

Tests

• go test ./pkg/observability
• go test ./global-gateway/cmd/global-gateway ./regional-gateway/cmd/regional-gateway ./cluster-gateway/cmd/cluster-gateway ./scheduler/cmd/scheduler ./ssh-gateway/cmd/ssh-gateway ./netd/cmd/netd ./netd/pkg/daemon ./manager/cmd/manager ./manager/cmd/procd ./storage-proxy/cmd/storage-proxy ./ctld/cmd/ctld