Add lts-do-call-me for Debian LTS

Most maintainers appreciate the help of the Debian LTS project with providing
security updates for their packages in oldstable releases.

However there are some maintainers who want either to be informed about
package changes in their packages or want to take care of any update themself.

Add a new list, lts-do-call-me, that contains all maintainers and/or source
packages that should be handled by the maintainer. Members from the LTS team
should always contact all maintainers in this list before starting to work on
the package.