mixin: networking overview renders useless panels for the gateway

Describe the bug

The networking overview dashboards renders the number of inflight request for the mimir gateway https://github.com/grafana/mimir/blob/1e903e4620504a265d49ccee621f09e17b3a18f8/operations/mimir-mixin/dashboards/overview-networking.libsonnet#L9 but the gateway(when using the non enterprise gateway which is nginx) will never expose the metrics used in those panel:

• Inflight requests (per pod) uses cortex_inflight_requests
• TCP connections (per pod) uses cortex_tcp_connections and cortex_tcp_connections_limit

Should those panels be removed for the gateway in the case that it uses nginx?

On that note, the rollout dashboard should probably be removable from the mixins as it's main use case it for the enterprise gateway

To Reproduce

Steps to reproduce the behavior:

1. Start Mimir (SHA or version)
2. Perform Operations(Read/Write/Others)

Expected behavior

A clear and concise description of what you expected to happen.

Environment

• Infrastructure: [e.g., Kubernetes, bare-metal, laptop]
• Deployment tool: [e.g., helm, jsonnet]

Additional Context