[APM] Custom links are not fetched after creating a new one from the transaction page

[cauemarcondes]

On the transaction detail page create a new custom action by clicking on the Actions button. After creating a new one, close the popover and open it again the item that has just been created is not shown until a full page reload happens.

custom.link.mov

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)