Use restart ReloadMode to support metrics reload
Use restart ReloadMode to support metrics reload

Without the explicit ReloadMode in the plugin manifest, Gerrit assumes
'reload' and does not correctly manage the metrics registration.

For this plugin the restart mode is good enough: no need to risk
the reload mode and incur into the metrics problem.

Change-Id: I38ac8864be96bbfcb9f8f052f398cae570e86c06

GerritCodeReview/plugins_plugin-manager,GerritCodeReview/plugins_plugin-manager,GerritCodeReview/plugins_plugin-manager