Add stage groups error budgets information to Sisense

In #977 (comment 551605990) it was mentioned that we should get this information as a Performance Indicator into Sisense.

However, in the past it has been difficult to get data from Prometheus/Thanos into Sisense (https://gitlab.com/gitlab-data/analytics/-/issues/7713).

One suggestion is to get the single number into a file (JSON, CSV), that can be consumed by Sisense

Status 2021-06-02

gitlab-com/runbooks!3581 (merged) Has been merged and a scheduled pipeline has been set up to run from ops.GitLab.net here: https://ops.gitlab.net/gitlab-com/runbooks/-/pipeline_schedules/181/edit

We're now looking into how to load that data into snowflake in https://gitlab.com/gitlab-data/analytics/-/issues/7713