Add course length default value

There was two options: Use FourYears like a enumerator or free text.
After giving too much thought I opt-in for free text as this will
unlikely to change in content

app/services/courses/creation_service.rb

@@ -39,6 +39,8 @@ def build_new_course
         course.can_sponsor_student_visa = false
         course.can_sponsor_skilled_worker_visa = false
         course.degree_grade = 'not_required'
+        course_enrichment = course.enrichments.find_or_initialize_draft
+        course_enrichment.course_length = '4 years'
       end
 
       AssignSubjectsService.call(course:, subject_ids:)

spec/features/publish/courses/new_tda_course_spec.rb

@@ -311,6 +311,8 @@ def and_the_tda_defaults_are_saved
     expect(course.additional_degree_subject_requirements).to be_nil
     expect(course.degree_subject_requirements).to be_nil
     expect(course.degree_grade).to eq('not_required')
+    expect(course.enrichments.last).to be_present
+    expect(course.enrichments.last.course_length).to eq('4 years')
   end
 
   def and_i_select_no_send

spec/services/courses/creation_service_spec.rb

@@ -37,6 +37,8 @@
       expect(subject.additional_degree_subject_requirements).to be_nil
       expect(subject.degree_subject_requirements).to be_nil
       expect(subject.degree_grade).to eq('not_required')
+      expect(subject.enrichments.last).to be_present
+      expect(subject.enrichments.last.course_length).to eq('4 years')
     end
   end