Document Package Signing Key management

From https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2632 , https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2632#note_36193600

Document the management processes for the package signing keys use for GitLab-provided packages.

created branch 10-document-package-signing-key-management

In https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2632#note_37059407, @pcarranza states

@WarheadsSE use the toolbelt directory if you think we should keep it close to our hearts. Else, there's a "scripts" directory too for unrelated things.

Should scripts just be actual scripts? Toolbelt seems to a be a series of bash alias/functions. This is more a documentation of step series, and not a file that can be run.

@WarheadsSE If it's documentation, then it should go in the howto section, explaining what is it about.

I know that this started as a place in which writing troubleshooting runbooks, but it has grown to be a replacement for the chef-repo/doc folder, so it makes sense to keep this documentation here.

mentioned in merge request !319 (merged)

mentioned in issue gitlab-org/omnibus-gitlab#2537 (closed)

marked this issue as related to gitlab-org/omnibus-gitlab#2537 (closed)

closed via merge request !319 (merged)