[ENH] Update instructions for changing passwords and the default deployment profile

[alyssadai]

• Docs update following [REF] Change default profile from local_node to full_stack recipes#86 and [REF] Create GraphDB password secrets from .txt files instead of env variables recipes#84

Changes proposed in this pull request:

• Default profile changed to full_stack
• Added instructions for using COMPOSE_PROFILES var in .env
• Updated instructions for changing admin/user passwords using .txt files

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[surchs]

Hey @alyssadai. Thanks for all the nice changes!

I disagree with the "here's how you change the default profile" bit. Let's not add that. More generally: let's not just tack a change like that onto an unrelated PR so we have a chance to first discuss it in an issue in the future.

Otherwise all good.

[surchs]

🧑‍🍳