Confluence should not create new jar files for user installed plugins in osgi-plugins-cache on every startup

Currently Confluence creates a new jar file in plugins-osgi-cache/transformed-plugins for every plugin that's been installed through the UPM. This is because Confluence pulls down the plugin from the database and always gives it a unique filename and modified date. The plugins system then does not use the cached version of the plugin and instead creates a new JAR. Under environments where Confluence is restarted often, this can take up a lot of disk space.