[2.8] Honor agent TLS mode when installing Fleet

[weyfonk]

Backport of rancher#45842 to 2.8.

Depends on fleet#2577.

Testing

Engineering Testing

Manual Testing

1. Installed Rancher via Helm, built locally using dev-script/build-local.sh:

$ helm upgrade --install rancher rancher-latest/rancher --devel \
    --namespace cattle-system --create-namespace \
    --set bootstrapPassword=admin \
    --set replicas=1 \
    --set hostname=172.17.0.2.sslip.io \
    --set rancherImageTag=2.8-test-strict-tls \
    --set extraEnv[0].name=CATTLE_CHART_DEFAULT_BRANCH \
    --set extraEnv[0].value=fleetci-dev-v2.8-20240703115101 \
    --set extraEnv[1].name=CATTLE_CHART_DEFAULT_URL \
    --set extraEnv[1].value=https://github.com/fleetrepoci/charts \
    --set extraEnv[2].name=CATTLE_FLEET_VERSION \
    --set extraEnv[2].value=999.9.9+up9.9.9

(whereby the Fleet version and charts branch were set by this workflow)

2. Found configmaps fleet-agent and fleet-controller, in namespaces cattle-fleet-local-system and cattle-fleet-system respectively, to contain the key/value pair "agentTLSMode": "system-store"

3. Navigated the Rancher UI at https://172.17.0.2.sslip.io/dashboard/c/local/explorer/configmap and edited config map rancher-config, adding a fleet field with value {"agentTLSMode": "strict"}

4. Could see the fleet-agent pod being re-created, and config maps fleet-controller and fleet-agent being updated with the new agentTLSMode value.

Automated Testing

N/A

QA Testing Considerations

Regressions Considerations

N/A