Add project setting to allow configuring another gitlab project's issue tracker

Proposal

As discussed here, we'd like to use the Create issue to resolve thread option when reviewing merge requests, however, we don't want to use the project's issue tracker, but instead use the gitlab-org/gitlab issue tracker.

The purpose of this issue is to add a new project configuration option, possibly at the following path:

.
└── Settings/
    └── General/
        └── Visibility, project features, permissions/
            └── Issues/
                └── Use another project's issue tracker

This option should allow us to specify another GitLab project's issue tracker, which will be used when creating issues via the resolve thread into follow-up issue in merge request comments: