be able to handle a "graphs" property in threads

Asked by nical

This property would hold an array of timestamps / values (or an array of these graphs if we want to support drawing several of them) that we could draw in the header. The goal for nical is to be able to add arbitrary graphs to more easily relate with the things we already capture.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-677)