Rename title-image to title_image

Usually, underscores are used for keys in a YML file as already done for
all other variables. Only the variable title-image used a minus so far.
This change replaces all occurences of title-image by title_image.
8 jobs for replace-minus-in-title-image in 3 minutes and 53 seconds (queued for 10 seconds)
Status Name Job ID Coverage
  Build
passed build:latest #103890

00:00:46

passed build:production #103893

00:02:41

passed build:production:review-apps #103892

00:02:41

passed build:production:subpath #103891

00:02:44

 
  Test
passed test:htmlproofer #103894

00:01:00

passed test:htmlproofer:subpath #103895

00:01:06

 
  Review
passed review #103896
review-apps

00:00:05

passed stop_review #103897
review-apps manual

00:00:02