Replace link CA… on the Relays page starts a replacement of the link CA
every relay shares, sent as replaceLinkCa on one relay. While it's under
way a line above the relays says since when and which relays it waits
for, with Finish now… and Cancel it…, and the page looks again every 15
seconds, as the server finishes it by itself. A relay that doesn't trust
the new CA yet says so on its card; one that only trusts a replaced CA
asks for a new join, and nothing else.
The action shows only for a server that sends linkCaReplacing.