Milestones depend on delivery promise configuration

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1. set_milestone : the acheived milestone. If empty, without_always_at_start milestone is set (generally de case when initiating milestones in the graph).

   1. To make use of milestones, they must be stored for the order at each of its line_item_groups claimed transition. To do so, the action set_milestone has to be set in the claim transition of the line_item_groups.

   2. When recomputing, solutions with non-achieved milestones dates in the future (greater than now) will be considered as valid options. Those with dates in the past, will not be considered.

2. set_milestone_alert : Schedule alerts to be triggered at milestones cutoffs (plus a delay)

   1. Notifications can be scheduled to be triggerd at the time of milestones cutoffs (plus a certain delay). When triggered, a validity check will be performed to ensure the specified milestone has not yet been reached/acheived. If already reached, notifications won't be triggered.

      1. The time at which the notification will be triggered is the milestone cutoff of the first milestone stored in order_delivery_promises. Cutoffs are sorted based on the sort criteria configured for the site.

   2. A special notification named recompute_cutoffs_sets can be called to recompute the cutoffs for each milestone.

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