Resolve "Error message is not helping when an include is not a valid URL or local path"

What does this MR do?

When an include defines a properly formed URL or a valid local path but with no content, the .gitlab-ci.yml parser fails without given a proper reason why.

Why was this MR needed?

To improve the error message return by the parser when an include statement is not valid

Screenshots (if relevant)

With a valid URL with no content (Pipeline view)

With a valid URL with no content (.gitlab-ci.yml view)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #4873 (closed) Closes #4874 (closed)