When GitLab issues disabled, issues tab should be gone, even if external issue tracker is on

Description

• Currently if GitLab issues is disabled, the issues tab is enabled if an external issue tracker integration is enabled.
• This should not be the case. The issues tab should be reserved only for GitLab issues.
• The issues tab should be only for GitLab issues. If GitLab issues is disabled in project settings, the issues tab should not appear, regardless of any other integrations.

Out of scope

• We should have a separate UI for any external issues tracker that a user turns on with integrations.
• That UI should be independent of GitLab issues.
• This allows users to turn on/off GitLab issues and external issue trackers independently.
• We should create separate issues for each external tracker to appear in our UI.

For example, one design could be like this: