Milestone 3: Update dashboard templates and prebuilt widgets

[narsaynorath]

To further increase discoverability of the new dataset and its capabilities, we'd like to add dashboard templates and prebuilt widgets that show off this functionality.

Specific widgets TBD, possibly close recreations of the insights modules.

[getsantry]

Routing to @getsentry/product-owners-dashboards for triage ⏲️