Show empty state for external CI config in pipeline editor

What does this MR do and why?

For #364030 (closed)

This adds a special empty state for when the user visits the pipeline editor when the project's CI config is located outside the project (either it's in another project or in another site). In these cases, the pipeline editor will not allow the user to edit the file since it doesn't have access to it.

Screenshots or screen recordings

State	Screenshot
🆕 When CI config is outside the repository (in an external project or remote location)
With no CI config
With a CI config in the same project

How to set up and validate locally

1. Follow the instructions to set your project's CI config to link outside the project. Refer to the examples in the docs.
   • To test for an CI config file located in another project, you can use .gitlab-ci.yml@group/project.
   • To test for a remote CI config file, you can use https://example.org/file.yml.
2. Go to the Pipeline Editor (CI/CD > Editor)
3. Verify that the empty state shows up without the CTA button.

MR acceptance checklist

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