feat: distributed scheduling for version check job (#13042)

This change spreads Chatwoot Hub version checks across the day by
scheduling each installation at a stable minute derived from its
installation identifier, instead of having all instances check at the
same fixed time.

Closes
-
https://linear.app/chatwoot/issue/CW-6107/handle-the-spike-at-12-utc-on-chatwoot-hub

What changed
- Added `Internal::TriggerDailyScheduledItemsJob` to act as the daily
trigger for deferred internal jobs.
- Updated the version check cron entry to run once daily at `00:00 UTC`
and enqueue the actual version check for that installation’s assigned
minute of the day.
- Used a deterministic minute-of-day derived from
`ChatwootHub.installation_identifier` so the check time stays stable
across deploys and restarts.
- Kept the existing cron schedule key while switching it to the new
orchestrator job.

How to test
- Run `bundle exec rspec
spec/jobs/internal/check_new_versions_job_spec.rb
spec/jobs/internal/trigger_daily_scheduled_items_job_spec.rb
spec/configs/schedule_spec.rb`
- In a Rails console, run
`Internal::TriggerDailyScheduledItemsJob.perform_now` and verify
`Internal::CheckNewVersionsJob` is enqueued with a `wait_until` later
the same UTC day.
- In Super Admin settings, use Refresh and verify the version check
still runs immediately.

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>

app/jobs/internal/trigger_daily_scheduled_items_job.rb

@@ -0,0 +1,25 @@
+class Internal::TriggerDailyScheduledItemsJob < ApplicationJob
+  queue_as :scheduled_jobs
+
+  def perform
+    # Schedule daily deferred jobs here so each installation can spread load
+    # across the day without changing its slot on deploys or restarts.
+    schedule_version_check
+  end
+
+  private
+
+  def schedule_version_check
+    return unless Rails.env.production?
+
+    Internal::CheckNewVersionsJob.set(wait_until: version_check_run_at).perform_later
+  end
+
+  def version_check_run_at
+    Time.current.utc.beginning_of_day + designated_minute.minutes
+  end
+
+  def designated_minute
+    @designated_minute ||= Digest::MD5.hexdigest(ChatwootHub.installation_identifier).hex % 1440
+  end
+end