[DOCS] Add `rollup.sequencerhttp` to node operation docs

[sbvegan]

Brief Description of the Docs Request

Add a callout on step 7, making sure people configure --rollup.sequencerhttp to their sequencer node.

HTTP endpoint of the sequencer. op-geth will route eth_sendRawTransaction calls to this URL. The OP Stack does not currently have a public mempool, so this is required if you want your node to support transaction submission.

Description of the Documentation You'd Like

Add callout to this page

Links to Related Pages

https://docs.optimism.io/builders/chain-operators/management/operations#adding-nodes

Additional Context

Provide any additional context about this documentation request. What problems did you run into that caused you to make this request?
Which existing documentation pages did you already try as a solution to your problem? Why do you think the requested page(s) will be beneficial to developers in the Optimism Collective?