Revisit rails_requests apdex SLO for git, api and web after urgencies have been set

In &573 We've added an SLI rails_requests to the "web", "api" and "git" services.

This SLI track if a request performed fast enough in comparison to it's target duration. The target duration can be customized, but defaults to 1 second.

This means that we've tightened the duration from the existing puma SLI, which is why we've had to lower the SLOs as follows:

• API: 0.985 down from 0.995
• Web: 0.992 down from 0.998
• Git: 0.997 down from 0.998

After the stage groups have had a chance to customize the durations on the endpoints they own, we should see if we can tighten up the SLOs again.