kubeseal: add page (#16030)

* Create kubeseal.md

* Update kubeseal.md

* Update kubeseal.md

Author: MachiavelliII

pages/common/kubeseal.md

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+# kubeseal
+
+> Client-side utility for encrypting Kubernetes secrets using the Bitnami Sealed Secrets controller.
+> Creates SealedSecret resources that can be safely stored in version control.
+> Requires a controller running in the cluster (e.g., installed via `kubectl apply -f controller.yaml`).
+> More information: <https://github.com/bitnami-labs/sealed-secrets>.
+
+- Encrypt a Kubernetes secret from a YAML file into a SealedSecret (default JSON output):
+
+`kubeseal < {{secret.yaml}} > {{sealedsecret.json}}`
+
+- Encrypt a secret, outputting it in YAML or JSON format, using a bearer token for API authentication:
+
+`kubeseal {{[-o|--format]}} {{yaml|json}} --token {{my-bearer-token}} < {{secret.yaml}} > {{sealedsecret.yaml}}`
+
+- Seal a secret using a specific controller namespace of sealed-secrets controller and name:
+
+`kubeseal --controller-namespace {{controller-namespace}} --controller-name {{controller-name}} < {{secret.yaml}} > {{sealedsecret.yaml}}`
+
+- Encrypt a raw secret value from a file with a specified name and scope:
+
+`kubeseal --raw --from-file {{path/to/secret.txt}} --name {{my-secret}} --scope {{strict|namespace-wide|cluster-wide}} > {{sealedsecret.yaml}}`
+
+- Fetch the controller's public certificate for offline sealing with basic auth:
+
+`kubeseal --fetch-cert --username {{username}} --password {{password}} > {{cert.pem}}`
+
+- Seal a secret offline using a fetched certificate:
+
+`kubeseal --cert {{cert.pem}} < {{secret.yaml}} > {{sealedsecret.yaml}}`
+
+- Merge a secret into an existing SealedSecret file in-place:
+
+`kubeseal --merge-into {{sealedsecret.yaml}} < {{secret.yaml}}`
+
+- Validate a SealedSecret without applying it:
+
+`kubeseal --validate < {{sealedsecret.yaml}}`