Fix Vikunja install script to prevent database deletion upon updating

[vhsdream]

Note

We are meticulous when it comes to merging code into the main branch, so please understand that we may reject pull requests that do not meet the project's standards. It's never personal. Also, game-related scripts have a lower chance of being merged.

Description

This PR addresses an issue in which the Vikunja database (and files folder if created) gets deleted when the user updates Vikunja via the script. The change adds two more substitutions via the sed command to modify the default Vikunja config file; changes the location of the database file and the files folder to /etc/vikunja.

Fixes #502

Type of change

Please check the relevant option(s):

• Bug fix (non-breaking change that resolves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (a fix or feature that would cause existing functionality to change unexpectedly)
• New script (a fully functional and thoroughly tested script or set of scripts.)

Prerequisites

The following efforts must be made for the PR to be considered. Please check when completed:

• Self-review performed (I have reviewed my code, ensuring it follows established patterns and conventions)
• Testing performed (I have tested my changes, ensuring everything works as expected)
• Documentation updated (I have updated any relevant documentation) - There is none, as far as I can tell.

Additional Information (optional)

Provide any additional context or screenshots about the feature or fix here.

Related Pull Requests / Discussions

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