Fix fleet status calculation

[torchiaf]

Summary

Fixes #11181

Occurred changes and/or fixed issues

When Rancher is freshly installed, it takes some time to create cattle-fleet-local-system/fleet-agent StatefulSet in local cluster.
We are excluding it from fleet agent health checks during this startup period.

Technical notes summary

During the startup period:

• cattle-fleet-local-system/fleet-agent is null
• Rancher is able to create and communicate with new downstream clusters
• cattle-fleet-system/fleet-controller is OK

So it's reasonable to calculate the fleet agent status using only cattle-fleet-system/fleet-controller and include cattle-fleet-local-system/fleet-agent when available.

Areas or cases that should be tested

• cluster explorer -> local -> Dashboard page -> Health boxes -> fleet

How to test

• Install Rancher 2.9.x
• Check the fleet health box (see screenshot)
• `cattle-fleet-local-system/fleet-agent is created by Rancher after ~5/10 minutes (docker installation)

Screenshot/Video

Checklist

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[aalves08]

LGTM