[REF] website_slides : refactor share_modal to use same template(s) in all case

This commit prepares the next one. It creates generic main and sub templates
for slide share modal.

In order to be usable for all cases, header and body sub template have been added.
Also and in the same purpose, as the website url can be another url
than the record to share (or if the record doesn't have website_url), this website_url
can be specified separately from the record. Otherwise, the standard behaviour is to
use the record.website_url.

Task ID: 1950396
PR #31776