Code Insights: use default values for insight templates
Created by: vovakulikov
Closes: https://github.com/sourcegraph/sourcegraph/issues/30947
Test plan
- Go to the get started page
- Click on the "use as template" link in the Insight Examples section
- See that in the creation UI you have a default value for the time step - 2 months
- Click on the "use as template" link in the Templates section
- See that in the creation UI you have a default value for the time step - 2 months
Bonus line: click "use as template" and fill out the repositories field. You should see the live preview. Prior to this PR, the live preview chart ignores the templates series. This PR fixes this.