[MM-15831] Improve system for storing status of available plug… (#11185)

* Move State property from activePlugin to PluginHealthStatus. env.activePlugins is now reserved for healthy running plugins.

* Add comments for function declarations

* Combine activePlugins and pluginHealthStatuses into a common structure, registeredPlugins

* Add check to see if plugin is active before deactivating it

* Make `Deactivate` set plugin status

* Add comment explaining the `registeredPlugins` map
* Give responsibility to set plugin disabled status upon deactivation back to `env.Deactivate`

* check if plugin needs to be deactivated before setting status

model/plugin_status.go

@@ -13,7 +13,7 @@ const (
 	PluginStateStarting            = 1 // unused by server
 	PluginStateRunning             = 2
 	PluginStateFailedToStart       = 3
-	PluginStateFailedToStayRunning = 4 // unused by server
+	PluginStateFailedToStayRunning = 4
 	PluginStateStopping            = 5 // unused by server
 )