Staged rollout

gps --package com.example.app --json tracks list
gps --package com.example.app tracks get production

gps --package com.example.app tracks promote \
  --from internal \
  --to beta \
  --confirm

gps --package com.example.app tracks rollout production \
  --user-fraction 0.1 \
  --confirm

gps --package com.example.app tracks rollout production \
  --user-fraction 0.5 \
  --confirm

gps --package com.example.app tracks halt production --confirm