Allow metrics in filters

[courtneyholcomb]

Resolves #273 Resolves SL-1849

Description

Allow users to reference metrics in where filters for metrics, measures, and saved queries. This uses syntax like: {{ Metric('metric_name', group_by=['entity_name', 'dimension_name']) }} = 10 This unlocks new types of metrics that users have been asking for. Some examples can be found in the linked issue and in this design doc.

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [x] I have signed the CLA
• [x] This PR includes tests, or tests are not required/relevant for this PR
• [x] I have run changie new to create a changelog entry

[github-actions[bot]]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[linear[bot]]

SL-1849 DSI: allow metrics in where filters