Magician vacation yaml

[trodge]

The main purpose of this PR is to move the vacation data into yaml so that it is easier to update and to consume from the good build approver.

I have also attempted to simplify the logic for determining if reviewers are on vacation and prevent after-hours reviews from being assigned at the beginning of vacations.

The intention is to allow adding vacations the old way for now and at some later point switch to using yaml exclusively.

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