feat(legend): implementation of legend for visualizations

Implemented a component that can be used by visualisations to display the legend. Left the specific implementation up to the visualisations. Future extensions can include scales (e.g., continuous, categorical) that can be passed as children.

requested review from @milho001

assigned to @s.a.vink

merged

mentioned in commit 7c11ca5f

This MR is included in version 1.6.0

The release is available on GitLab release.

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