charts: href option to link to the grafana

Do you think that it would be possible to also add a href option for this to still be able to link to the grafana when clicking on a chart? :)

_Originally posted by @maurerle in https://github.com/freifunk/meshviewer/issues/388#issuecomment-4741839771_

Currently, it is not possible to link somewhere from the charts anymore, when only using charts.

Locate the chart component and inspect how chart clicks are currently handled, then check how Grafana links were supported before charts were introduced. Add an href option that preserves navigation to Grafana when a chart is clicked, and verify that charts with and without href behave correctly.

Written by the indexing model from the issue text.