Added 2 important acquisition/retention metrics.
Split 'common/' into commit '60cf50938d2b0463786659f349827c714695345c'

git-subtree-dir: common
git-subtree-mainline: a8eab8e557d77cfa3428a85f0afd95e47a5e9656
git-subtree-split: 60cf50938d2b0463786659f349827c714695345c
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