Add Budget Category enumeration

Replacing ‘activity’ on budget type with this—they should come from a
user’s role rather than the activity. Going with a generic name though
so this can change over time.

app/models/time_budget_category.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class TimeBudgetCategory < Enumeration
+  has_many :time_budgets, foreign_key: :category_id
+
+  OptionName = :enumeration_time_budget_category
+
+  def option_name
+    OptionName
+  end
+end

config/locales/en.yml

@@ -1,3 +1,5 @@
 en:
   field_jobs: Jobs
   field_job: Job
+
+  enumeration_time_budget_category: Time budget categories