[FIX] mail, web_editor: allow tel links in email templates (#24926)

Before this commit: links like `tel:+1-555-555-5555` were being replaced
both in javascript (prefixing `http`, when using the summernote editor)
and python (prefixing the base url, when they were added directly to the template).

After this commit: the replacement is avoided on links with `tel` scheme.

This is related to commit: 8b97a399