Trigger status push on plugin status change

[sspaink]

StatusPlugin only reports on the periodic schedule. OPA Go also pushes a status update whenever a plugin transitions state (e.g. bundle activation, download failure), so dashboards see transitions promptly instead of waiting up to a full interval.

• Hook into PluginManager.updatePluginStatus so a status transition triggers an immediate report (debounced if multiple plugins change in a short window).
• Don't reset the periodic schedule — the eager push is in addition to it.
• Make the eager-push behavior configurable (default on, matching OPA Go).
• Tests: state transition causes a report inside the debounce window; sustained transitions don't flood the upstream.