Doc: Add Fleet submariner plugin doc (kurator-dev#668)

* add plugin doc

Signed-off-by: Tom <[email protected]>

* add subctl check

Signed-off-by: Tom <[email protected]>

* update submariner doc

Signed-off-by: Tom <[email protected]>

---------

Signed-off-by: Tom <[email protected]>

docs/content/en/docs/fleet-manager/submariner-plugin.md

@@ -0,0 +1,100 @@
+---
+title: "Enable multi cluster networking with Submariner"
+linkTitle: "Enable multi cluster networking with Submariner"
+weight: 20
+description: >
+  The easiest way to manage multi cluster submariner plugin with fleet.
+---
+
+In this tutorial we’ll cover the basics of how to use [Fleet](https://kurator.dev/docs/references/fleet-api/#fleet) to manage submariner plugin on a group of clusters.
+
+## Prerequisites
+
+1. Setup Fleet manager by following the instructions in the [installation guide](/docs/setup/install-fleet-manager/).
+
+2. Running the following command to create two secrets to access attached clusters.
+
+```bash
+# Create secrets for the attached clusters
+kubectl create secret generic kurator-member1 --from-file=kurator-member1.config=/root/.kube/kurator-member1.config
+kubectl create secret generic kurator-member2 --from-file=kurator-member2.config=/root/.kube/kurator-member2.config
+
+# Label a gateway node for each attached cluster
+kubectl label node kurator-member1-control-plane submariner.io/gateway=true --kubeconfig=/root/.kube/kurator-member1.config
+kubectl label node kurator-member2-control-plane submariner.io/gateway=true --kubeconfig=/root/.kube/kurator-member2.config
+```
+
+### Create a fleet with metric plugin enabled
+
+`SUBMARINER_PSK` needs to be set as described in [here](https://submariner.io/operations/deployment/helm/).
+
+```bash
+export SUBMARINER_PSK=$(LC_CTYPE=C tr -dc 'a-zA-Z0-9' < /dev/urandom | fold -w 64 | head -n 1)
+
+envsubst < examples/fleet/network/submariner-plugin.yaml | kubectl apply -f -
+```
+
+After a while, we can see the fleet is `ready`:
+
+```bash
+kubectl wait fleet quickstart --for='jsonpath='{.status.phase}'=Ready'
+```
+
+### Verify the Installation
+
+To ensure that the Submariner plugin is successfully installed and running.
+
+Run the following commands:
+
+```bash
+kubectl get pod -n submariner-operator --kubeconfig=/root/.kube/kurator-member1.config
+kubectl get pod -n submariner-operator --kubeconfig=/root/.kube/kurator-member2.config
+```
+
+More detailed verification steps can be done as follows:
+
+> `subctl` needs to be installed to perform checks, please refer to the [Install subctl](https://submariner.io/operations/deployment/helm/#install-subctl).
+
+- Diagnostic checks:
+
+Perform `subctl diagnose` on each cluster:
+
+```bash
+subctl diagnose all --kubeconfig /root/.kube/kurator-member1.config
+```
+
+- Verify the connectivity between the clusters:
+
+```bash
+export KUBECONFIG=/root/.kube/kurator-member1.config:/root/.kube/kurator-member2.config
+subctl verify --context kurator-member1 --tocontext kurator-member2
+subctl verify --context kurator-member2 --tocontext kurator-member1
+```
+
+## Cleanup
+
+Guides for you to clean up the fleets and plugins.
+
+### 1. Cleanup the Submariner Plugin
+
+Tutorial for manual uninstallation can be found in Sumariner Documatation [here](https://submariner.io/operations/cleanup/#manual-uninstall).
+
+> Deleting the cluster to start from scratch is **recommended** because potential crd dependencies conflicts and some hard-to-find legacy resources or settings.
+
+### 2. Cleanup the Fleet
+
+When the fleet is deleted, all associated plugins will also be removed:
+
+```bash
+kubectl delete fleet quickstart
+```
+
+### 3. Cleanup the Infrastructure
+
+Uninstall fleet manager:
+
+```bash
+helm uninstall kurator-fleet-manager -n kurator-system
+```
+
+{{< boilerplate cleanup >}}