Automatically subscribe alert users to appeals cases when filed

[mlissner]

I'm subscribed to alerts for the district court case here:

https://www.courtlistener.com/docket/17211300/hachette-book-group-inc-v-internet-archive/

And it was appealed here:

https://www.courtlistener.com/docket/67801014/hachette-book-group-inc-v-internet-archive/

In the appellate case, we have the originating court information:

You can see in the screenshot we even are able to provide a link to look it up. If you click that link, it works marvelously:

Jeez, why don't we do this automatically? The system we need would:

1. Look at any new "originating court information".
2. If it contained the docket number and court, look it up with a simple search.
3. If there's one match:
   • Subscribe people to it if they are subscribed to the match.
   • Send an email saying, "You have been automatically subscribed." Email should include:
     • Links to the lower and upper court cases.
     • An explanation of why this is happening.
     • A link to unsubscribe to the appellate case.

This is a pretty small feature that'd have a really nice benefit.