~"Review::P3" is now the default label for all incoming Merge Requests,
whilst ~"Review::P2" are for high impacting Merge Requests but not as
much as when compared to ~"Review::P1"

This idea cam when we started discussing
`gitlab-org/gitlab-runner!1164` we
said this is the highest ~"Review::P2" but not quite ~"Review::P1"
because we want don't want to breach out SLO for ~"Review::P1" where we
have more than 1 ongoing Merge Request.

This gives us finer control of what is "next" after we finish the
~"Review::P1" or if they are blocked we can start working our way
through ~"Review::P2"