Enable `trace_memory_allocations` by default

This enables `trace_memory_allocations`
by default

changelogs/unreleased/enable-trace_memory_allocations.yml

+---
+title: Enable `trace_memory_allocations` by default
+merge_request: 55369
+author:
+type: changed

config/feature_flags/development/trace_memory_allocations.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/299524
 milestone: '13.9'
 type: development
 group: group::memory
-default_enabled: false
+default_enabled: true

lib/gitlab/memory/instrumentation.rb

@@ -25,7 +25,7 @@ module Gitlab
       def self.ensure_feature_flag!
         return unless available?
 
-        enabled = Feature.enabled?(:trace_memory_allocations)
+        enabled = Feature.enabled?(:trace_memory_allocations, default_enabled: true)
         return if enabled == Thread.trace_memory_allocations
 
         MUTEX.synchronize do