fix(helm): grafana dashboard: fix heatmaps to actually be heatmaps, not time series (#5069)

* chore(helm): grafana dashboard: upgrade to grafana v12 format.

Simply saving without performing modification.

Signed-off-by: Cédric de Saint Martin <cdesaintmartin@wiremind.io>

* fix(helm): grafana dashboard: fix heatmaps to actually be heatmaps, not time series

Also add units for webhook latency, and set max data point for those small widgets

Signed-off-by: Cédric de Saint Martin <cdesaintmartin@wiremind.io>

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Signed-off-by: Cédric de Saint Martin <cdesaintmartin@wiremind.io>
Co-authored-by: Gergely Brautigam <182850+Skarlso@users.noreply.github.com>