Add ability to add dependencies on tasks

[malini]

We should add a "Depends on" column that can have 1 or more dependent tasks

[malini]

After chatting with Andrei: We can make the All Github Issues db self-referential and using sub-issues in GH. Then, we can update the notion scripts so that once it updates the github database with all issues, it does a second pass over all the sub-issues, and will update the self-referencial dependencies column with tasks. This way, we won't have to worry about whether or not a task exists in the db yet or not, as we do a first pass to push all issues in the db, and then modify the dependencies column