cubicweb-vcreview #5359034 add a transition for Patch to "decline" review [in-progress]

For many reason, one may want to decline the review of a patch (no time, lack of technical background, lack of interest in the project). Rather than either ignoring the patch or just accepting it without actual review, declining review would clearly indicate than the review will no be made. Upon fire of this transition, a new reviewer would be selected.

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patchAdd a "decline review" transition [reviewed]