[EE] App label warning for deploy boards

What does this MR do?

Show warning if any deployments has label app=CI_ENVIRONMENT_SLUG. Note the warning won't show if there's an app label where the value does not match CI_ENVIRONMENT_SLUG

Dependent on https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14020

CE Backport MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29740

https://gitlab.com/gitlab-org/gitlab-ee/issues/11209

Manual QA

Scenario	Screenshot	-
Auto DevOps deployment		✅
Auto DevOps deployment + nginx with app=production label		✅
nginx with app=production label (fixed)		✅

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team