[IMP] website_slides: Slide form view revamp

This commit improves the user experience in the slide.slide
form view by reorganizing fields, renaming fields and  hiding
unnecessary fields.

This commit also introduces two  new fields:
 - comment_count: computed field that gets the number of comments on the slide
 - channel_allow_comment: Related field to the channel_id.allow_coment.
                          This field is used to hide/show unnecessary fields

TaskID: 1978736
PR: #34232