Allow toggling dedicated_redis_trace_chunks per project

app/models/ci/build_trace_chunk.rb

@@ -14,8 +14,14 @@ module Ci
 
     belongs_to :build, class_name: "Ci::Build", foreign_key: :build_id
 
-    default_value_for :data_store do
-      if Feature.enabled?(:dedicated_redis_trace_chunks, type: :ops)
+    default_value_for :data_store do |chunk|
+      # We're using the safe operator here to get to the project for which we're
+      # creating a TraceChunk because the build attribute would not be populated
+      # when the chunk was initialized by FactoryBot:
+      # https://github.com/thoughtbot/factory_bot/wiki/How-factory_bot-interacts-with-ActiveRecord
+      # While the `default_value_for` gem depends on an `after_initialize`
+      # callback.
+      if Feature.enabled?(:dedicated_redis_trace_chunks, chunk.build&.project, type: :ops)
         :redis_trace_chunks
       else
         :redis