As a cluster-administrator, I want to know what gateway configurations are supported in the ServiceMeshControlPlane, so that I can configure the SMCP for my mesh.

Create a module to document the configuration settings in under `spec.gateway` in the SMCP and add it to the ossm-reference-smcp.adoc assembly file.

GitHub reference documentation - https://github.com/maistra/api/blob/maistra-2.1/docs/crd/maistra.io_ServiceMeshControlPlane_GatewaysConfig_v2.adoc