Update the horde drones to use the agent checkin timeout request parameter

[cmacknz]

Issue

The changes in #2408 update the agent to report its configured checkin timeout to Fleet Server. When this parameter is set, Fleet server will dynamically set the server side timeout to the agent's checkin timeout minus 2 minutes. This makes it so that the agent always gets a complete response from Fleet server before its request times out. See elastic/fleet-server#2491.

Update the horde drones to use this new 7m timeout in our Fleet scale tests to ensure there are no unintended side effects of this change at scale.

Definition of done

• Horde drones are now using the new 7m timeout for our Fleet Scale tests

[cmacknz]

@pchila this could also be considered a blocker for merging #2408 since we wouldn't want to release without this test.

It may be simpler to merge #2408 with the use of the checking request parameter removed so that we are guaranteed to have the previous behavior, and then we could put the parameter back once we have scale tests proving there are no surprises.

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)