Improve readability for the up.sh script

[rafafrdz]

Problem

The up.sh script was functional but not very readable. This change is aimed at improving its clarity and maintainability.

Solution

Refactored the up.sh script to make the use of environment variables more explicit and easier to follow. This is a readability improvement only, no change in functionality or behavior.

One-line summary: Improve readability of up.sh by making environment variable usage more explicit.

Checklist

• You've signed-off your work
• Your changes are accompanied by tests (if relevant)
• Your change contains a small diff and is self-contained
• You've updated any relevant documentation (if relevant)
• You've included a one-line summary of your change for the CHANGELOG.md (Depending on the change, this may not be necessary).
• You've versioned your .sql database schema migration according to Flyway's naming convention (if relevant)
• You've included a header in any source code files (if relevant)

[boring-cyborg]

Thanks for opening your first pull request in the Marquez project! Please check out our contributing guidelines (https://github.com/MarquezProject/marquez/blob/main/CONTRIBUTING.md).

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