[MM-13507] Plugin framework: auto-restart plugins that crash (#10781)

* introduce plugin health check

* implement plugin health check job

* add support for checking pid of plugin process and RPC ping, to determine a plugin's health

* implement restart policy with back-offs

* support "EnableHealthCheck" boolean from config file.

* add tests for supervisor.PerformHealthCheck() and shouldDeactivatePlugin()

* improve error handling. clean up if blocks to be more concise

config/default.json

@@ -414,6 +414,7 @@
     "PluginSettings": {
         "Enable": true,
         "EnableUploads": false,
+        "EnableHealthCheck": true,
         "Directory": "./plugins",
         "ClientDirectory": "./client/plugins",
         "Plugins": {},