[REF] Update production deployment docs

[surchs]

• Closes Update docs for production #347

Changes proposed in this pull request:

These changes correspond to changes in the recipe repo: neurobagel/recipes#162

• changed the configure a node docs page
  • focus on "guide" style, meant to be read top to bottom
  • only two launch profiles: node and portal
  • only one proxy server recipe (nginx+acme) to keep it simple
  • reference of environment varibles moved to the end. more of a regular "docs" section
  • section on "security relevant variables" moved inside the "node" profile
  • additional section for how to launch the services behind existing proxy
  • strongly encourage each deployment starts from a fresh recipe clone (no longer "extension" of getting started)
• simplified the getting started docs page because prod deployments now always start from a fresh deployment
  • now just about getting user started locally (prod deployments are now completely separate)
  • replaced most clarifications and context with top-level admonition about prod deployment

Note

• NB_API_QUERY_URL is now only used for "getting started" and thus set to localhost:8000 to make the initial launch easier. For prod deployments, NB_API_QUERY_URL is composed automatically from other ENV variables
• there is now a new, dedicated compose file for "behind existing proxy". This makes setup easier and keeps the docs aligned.

Checklist

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