A budget is a plan that describes what you expect to spend on Cloud
projects, plus the rules to execute as spend is tracked against that
plan, (for example, send an alert when 90% of the target spend is met).
Currently all plans are monthly budgets so the usage period(s) tracked
are implied (calendar months of usage back-to-back).
User data for display name in UI. Validation: <= 60 chars.
Required. Budgeted amount.
Optional. Rules to apply to all updates to the actual spend,
regardless of the thresholds set in threshold_rules.
