Preview dag command

[alvinwanyeki]

• i know there's already lea docs that shows you the whole project's dag, but it would be helpful to have a command to quickly view a specific view's lineage.
• it could either be a new command lea tree or lea run --tree (though this might be confusing?).
• this might look something like:

$ lea tree +orders+

core.orders
├── [upstream]
│   ├── staging.orders
│   └── staging.payments
└── [downstream]
    └── report.delivered_orders