Fix broken API::Dora::Metrics speсs

What does this MR do?

By default dora4 metrics controller returns data for last 3 months

We use 2021-01-01 as fixture date in specs.

So controllers stoped returning this data on 2021-04-02

Also, max range was calculated as 91 days, while it's actually possible to have 92 days in 3 months. I caught this trying to fix the issue

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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Related to #326799 (closed)