Fixed the issues related to the GDI-DE compliance.

[ahmdthr]

The current generated ISO metadata conforms to the ISO-19139 standards, but fails the GDI-DE compliance. This PR aims to fix the GDI-DE compliance issues.

Checklist

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[ridoo]

@ahmdthr As discussed last week: Move the fixes to thuenen_atlas project. Let's decide in the Sprint meeting today to make upstream issue plus PR or not.

[ridoo]

Will be merged into thuenen_atlas: https://github.com/Thuenen-GeoNode-Development/Sprints/issues/6