Geo: When a secondary becomes a primary, destroy the OAuth application
Currently, when a secondary becomes a primary, the OAuth application is disassociated from that Geo node. I think we can go one step further and destroy it.
Additionally, if the node becomes a secondary, a new OAuth application is created, instead of reassociating with the old one.
https://gitlab.com/gitlab-org/gitlab-ee/blob/52a42336/ee/app/models/geo_node.rb#L265