New subscription support with cli

[akhilmhdh]

Description

Right now subscription is a cron job. At midnight it scans through all documents and previous one and runs the functions to find changes. Then if changes send mails to all subscribers.

New system

Now that cli is there we dont need a cron job anymore. Rather when cli is submit we run a job. We do a check for changes and then all required rule. We do send notification but its two step.

1. We will send notification to creators along the changes happening.
2. We will also send to subscribers notifying the changes.