[REF] Combine Stardog and graphDB setup instructions

[surchs]

Closes #74
Closes neurobagel/api#119
Closes #93

Changes proposed in this pull request:

• Added Linked tabs to group instructions for graphDB and Stardog separately across the page
• changed all references to generic database user to DBUSER (and example password to DBPASSWORD) -> maybe we should not keep the password the same to discourage people from actually sticking with it 🤔
• Small typo fix for data upload script example, discovered by @alyssadai

Checklist

• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF]) (see https://neurobagel.org/contributing/pull_requests for more info)
• PR links to GitHub issue with mention Closes #XXXX
• Checks pass

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[rmanaem]

Thanks for the PR @surchs. I left one comment, see if it should be addressed other than that good to go! 🧑‍🍳