UI: edges should come in/out to Promote buttons

[jessesuen]

In the following DAG, the edges coming out of the node come from the top and bottom of the upstream node. Because of that, they are disconnected from the PromoteSubscribers button.

Since the intent of the PromoteSubscribers button is to promote to downstream, I feel the edges should originate out of the button as a better visual indicator of what will be affected..

It seems possible because Argo CD can do it (and we use the same DAG library):

Also, maybe we should use this chance to make the promote subscribers more obviously a button. I think it may not be clear.

[jessesuen]

For some reason, the left side didn't get the same treatment as the right, so reopening

EDIT: probably that reason is because I only asked for PromoteSubscribers in the title and not Promote 🤦‍♂️ . But I actually meant both. Sorry for not being clear!