Add incoming test reports WebSocket feed

[preaction]

We should have a WebSocket feed available for reports as they come in from testers. This feed can be used by users to get test results just as quickly as they are generated, and they can be used by the backend to trigger processing jobs as data arrives, removing the need for a cron job and improving the processing speed of the site.

This requires that we have a test report document format defined (#5). The legacy Metabase API will need to write to this feed, so we will need a translation from the Metabase structure to the new structure. This translation will need to be used in quite a few places until the existing data can be migrated.