Ability to define a dimension / measure sets for easier reuse of dimension / measure definitions across dashboards

[AndrewRTsao]

As the number of dashboards and dimensions / measures grow, there will be situations where the developer will want to reuse existing dimensions and/or measures that have been defined in multiple dashboards. The assumption is that the developer will ensure that the appropriate dimension / measure exists and is appropriately defined in the underlying model. However, when using these same dimensions / measures across many dashboards, this can become increasingly painful to manage (as the number of dashboards grow). Furthermore, making changes to one dimension (e.g. changing the label or description slightly) would require copy-pasting these same changes across all these dashboards, which can be time consuming and tedious.

More details in this Slack thread: https://rilldata.slack.com/archives/C05693FLY7Q/p1707500508682199