add gradual rollout mechanism for history-v1 rollout GitOrigin-RevId: 5fa69f5c3874bd5df1f31fdd3115e4ba6a0dab51
[history-v1] backup-deletion-app: initial revision GitOrigin-RevId: 9e05c0e16595cb8d180861ef503c7b4522110d39
GitOrigin-RevId: ef2ef77e26df59d1af3df6dc664e284d3c70102d