Fetch logs for the GDK report in a more generic way

What does this merge request do and why?

Currently, we are using a hardcoded list of service names to fetch related logs. This MR takes a more generic approach and uses all the files located in the respective log directories. The only exception is log files, which are actively used since loading their content would result in an error.
Related issue.

How to set up and validate locally

1. Run gdk report.
2. Verify that the report contains more log content than before, especially logs from gitlab.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This MR references an issue describing the change.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.