./bin/package-operations should gracefully handle non-existent repo

Running the weekly checks today I encountered a failure not previously observed. Specifically, there was an ELA reserved for rails and the corresponding rails entry in packages.yml has a VCS link, but that link leads nowhere (i.e., the project does not exist and it leads to a 404). This causes the script to choke and bail out. Instead, this should be an expected condition (like, e.g., missing git tags) that the script reports on (for the specific contributor, as for other conditions) and then continues.

This also requires corresponding updates to the email template and to the two GitLab issue templates (one for the Salsa lts-updates-tasks project and the other for the GitLab extended-lts project).

Please put me as the reviewer for all relevant MRs.

/cc @santiago