Geo: Removing Geo nodes in the admin area

As was discussed in https://gitlab.com/gitlab-org/gitlab-ee/issues/9608 we need to deny removing a primary node without removing all the secondaries first.

Following on that, we could disable "Remove" and have a tooltip like "Cannot remove a primary node if there is a secondary node" to make it really explicit.

When you remove the primary node from the API, it should return an error if there are any secondaries left.

Proposed design

• The remove button is disabled if there are secondary nodes.

Reference

• disabled button - behavior
• disabled button - component