Imrpove model validation when adding spent time

We recently added support for setting timelog summary using the
API, but the validation error simply statse `invalid`. This MR
ensures the parent issuable validation error details the child
(timelog) error messsage e.g. timelog.summary: is too long
(maximum is 255 characters).

Changelog: changed

app/models/concerns/time_trackable.rb

@@ -20,7 +20,7 @@ module TimeTrackable
     validates :time_estimate, numericality: { message: 'has an invalid format' }, allow_nil: false
     validate  :check_negative_time_spent
 
-    has_many :timelogs, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+    has_many :timelogs, dependent: :destroy, autosave: true # rubocop:disable Cop/ActiveRecordDependent
   end
 
   # rubocop:disable Gitlab/ModuleWithInstanceVariables

spec/models/issue_spec.rb

@@ -31,6 +31,7 @@ RSpec.describe Issue do
     it { is_expected.to have_and_belong_to_many(:self_managed_prometheus_alert_events) }
     it { is_expected.to have_many(:prometheus_alerts) }
     it { is_expected.to have_many(:issue_email_participants) }
+    it { is_expected.to have_many(:timelogs).autosave(true) }
 
     describe 'versions.most_recent' do
       it 'returns the most recent version' do