Backend: Improve the error messaging when fetching remote includes are timing out

Summary

Some users have been receiving a timeout error when using remote includes. In an effort to help the user understand when remote include references are timing out, this issue is to improve the error messaging that is displayed when this scenario occurs.

Solution

By returning an appropriate error messaging when remote include references are timing out, it will enhance the user experience so that the user understands what is happening and can take appropriate actions.

backend will change the message in yaml_errors to be Request timed out when fetching configuration files. (still weight 1)
frontend will update the actual UI component, which includes the title --> (Can be done by backend in the same MR since this is a haml update).

New error text should be:

Unable to create pipeline

Request timed out when fetching configuration files.

We will remove the link to CI Lint from the error since it doesn't provide additional context about the error.

Implementation

Work Type	Description	Issue link
	NOTE: 🚨 All below issues can be done in parallel
backend	Backend: The gitlab-ci.yml is limited to 100 includes	#207270 (closed)
backend	Backend: Remove N+1 for Gitaly requests when fetching includes	#344829 (closed)
backend frontend	Improve the error messaging when fetching remote includes are timing out	👈 You are here
backend	Backend: Improve CI Linter performance through parallelizing HTTP calls	#351250 (closed)
backend	Backend: Caching includes to improve performance when using remote includes	#351252
backend	Backend: Batch request calls to Gitaly when fetching include	#382531 (closed)
backend	Backend: Group files by projects in config_file_project_validate_access	#382751 (closed)