[Cilium v1.19] fix: adapt Hubble/Cilium control plane for v1.19

[nddq]

Summary

Part 6 of the Cilium v1.19 upgrade (#1788).

Adapts Hubble daemon, K8s cell (cell_linux.go - 348 line refactor), monitor agent, hubble parsers, managers. Core changes: hubblecell.Core → hubblecell.Cell, kvstore client stub, slog throughout.

Files (25):

• cmd/hubble/cells_linux.go, cmd/hubble/daemon_linux.go, cmd/hubble/daemon_main_linux.go
• cmd/standard/daemon.go
• pkg/k8s/cell_linux.go, pkg/k8s/apiserver_linux.go, pkg/k8s/watcher_linux.go, pkg/k8s/placeholders_linux.go, pkg/k8s/local_node_synchronizer_linux.go
• pkg/hubble/parser/parser_linux.go, pkg/hubble/parser/layer34/parser_linux.go, pkg/hubble/parser/seven/parser_linux.go
• pkg/monitoragent/cell_linux.go, pkg/monitoragent/monitoragent_linux.go
• pkg/config/hubble_config_linux.go
• pkg/managers/pluginmanager/cells_linux.go, pkg/managers/pluginmanager/pluginmanager.go, pkg/managers/pluginmanager/pluginmanager_test.go
• pkg/managers/controllermanager/controllermanager.go, pkg/managers/controllermanager/controllermanager_test.go
• pkg/servermanager/cell_linux.go
• pkg/shared/telemetry/cell_linux.go
• pkg/controllers/daemon/nodereconciler/cell_linux.go, pkg/controllers/daemon/nodereconciler/node_controller_linux.go

Estimated size: ~800 lines

Depends on: #2034
Parent issue: #1788