Update page on deploying w/ existing proxy to include all steps for a production `node` or `portal`

[alyssadai]

Many of the profile-specific steps on the production deployment page are proxy-related env var configurations (e.g., setting domain, path). If using an existing proxy, these steps would be irrelevant and should be skipped. So, rather than linking to these sections, we should update the page on deploying using an existing proxy to have an equivalent set of node and portal setup instructions, just without the proxy-related steps.

This also reduces the burden on the user to navigate back and forth between multiple pages and keep in mind what steps to skip.

[github-actions]

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