Updates security issue and MR templates

Mayra Cabrerarequested to merge
update-security-templates into master

What does this MR do?

Omnibus is moving its security development from dev.gitlab.org to a project in a private group (Security), as first step, issue and merge request templates are being updated to reflect this.

Related to gitlab-com/gl-infra/delivery#692 (closed)

Edited by GitLab Release Tools Bot

Merge request reports