Set GPKG's to read-only explicitly, instead of the base volume.

[gerdos82]

Description

Set GPKG's to read-only explicitly, instead of the base volume. A read-only base volume can lead to issues if - for instance - a configmap is mounted on a subpath of the base volume. This is specifically an issue with the WFS and a custom mapfile.

Type of change

• Bugfix

Checklist:

• I've double-checked the code in this PR myself
• I've left the code better than before (boy scout rule)
• The code is readable, comments are added that explain hard or non-obvious parts.
• I've expanded/improved the (unit) tests, when applicable
• I've run (unit) tests that prove my solution works
• There's no sensitive information like credentials in my PR