[Uptime][Meta] Migrate uptime to new platform

[andrewvc]

This issue is to track work moving uptime to the new platform. See #40768 for more info

[elasticmachine]

Pinging @elastic/uptime

[justinkambic]

@andrewvc thanks for taking the initiative to start this process. I think we should define a GA target for this, since it's one of several items on our roadmap that has a hard deadline. We should also coordinate with other Observability teams because they've done considerable work already that we can duplicate for Uptime.

[justinkambic]

So here's an update on where we are with new platform migration:

The path for us is fairly straightforward.

1. We need to shim the references to legacy Kibana core (ui, chrome, etc) on the client
2. We need to shim the modules and functions supplied by Hapi/Kibana on the server side

At that point we will be able to drop in the new core when it's ready and move our plugin out of the legacy x-pack directory. This work is ongoing, the PR's can be tracked here:

client: #44722
server: #44938

[andrewvc]

Closing in favor of #39797