Enable use of line charts on metrics dashboard

Problem to solve

We are working to add additional chart types to GitLab, and we therefore need a way to define which type you want for a given chart. We can start with adding this support in YML based definition and database schema, and then add the option in the UI when we build the chart designer: https://gitlab.com/gitlab-org/gitlab-ee/issues/4452.

The scope of this issue is to add support enabling line charts on our metrics dashboards.

Intended users

• Delaney, Development Team Lead, https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#delaney-development-team-lead
• Sasha, Software Developer, https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer
• Devon, DevOps Engineer, https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer
• Sidney, Systems Administrator, https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sidney-systems-administrator
• Sam, Security Analyst, https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sam-security-analyst

Further Details

This supports the Metrics vision.

Proposal

As part of our effort of supporting all kinds of charts in our monitoring dashboards, we need to add support for line charts following the design pattern linked.