Cycle Analytics: second iteration

Description

We've shipped Cycle Analytics in 8.12 and we'll make it better in 8.13.

Specifications for devs

• Priority: The difference with the old flow is that the first commit that we track, should not be linked to something that has been pushed to production - in the given time range.
  • We need to measure everything that happened in the given time range, not only what's been pushed to production.
  • All stages except staging and production will basically remain the same.
  • The staging and production stages will only take into account the issues that have been pushed to production.
  • We should make sure that the explanation on the last two stages (staging and production) are clear.

Differences with the initial design

• Still no chart parts: not sure we can ship it for 8.13
• No code coverage at the top: not sure that this information belongs here
• No Percent 95th: I don't find this information useful at this time

References:

• Cycle analytics first iteration: https://gitlab.com/gitlab-org/gitlab-ce/issues/21170