docs: Database Lab tutorial fixes

Description

• Split code blocks for frictionless copy-pasting
  • -y and openssl req interactive CLI blocks execution of later lines
  • wait for Postgres startup required between docker run and initdb
• Mention promotion script

Related issue

Examples

Checklist

• the MR description has been reviewed
• this MR contains text changes and they have been reviewed OR there are no texts changes
• this MR contains GUI/CLI changes and they have been reviewed OR there are no GUI/CLI changes
• this MR contains API changes and they have been reviewed OR there are no API changes