Cache support for Plugins Manager

[AmmarAbouZor]

Currently, plugins manager scans plugins directory on app start loading each plugin to get its metadata and configurations schema and other needed data. This could affect startup time in case of many plugins, even if users won't be using those plugins.
caching the plugins info in a file while keeping track on the changes in plugins will avoid loading the plugins on each start up.

Note: This has lower priority than the other tasks in Step 1