We had a validation rule for milestones which made sure either the
status or the description was present. However, since the description is
now translatable, the validation error wasn't being displayed in the
admin form.
Moving the validation rule to the translation object fixes the problem.
However, the translation object needs to check an attribute in the
milestone object in order to know whether the description is required or
not. This is tricky because by default it loads the milestone object
from the database, meaning it doesn't work with new records and it
ignores params sent by the browser.
The solution is to manually assign the globalized model before
validating the object. It's a hack, but apparently Rails doesn't provide
a better way to handle this case [1].
[1] https://github.com/rails/rails/issues/32024
Generalize the BudgetInvestmentStatus model to Milestone::Status so it
is not specific to budget investments, but can be used for any entity
which has milestones. This is in preparation to make the Milestone
model polymorphic and usable by entities other than budget investments.
