Lazy load xterm css custom colors file

What does this MR do?

Lazy load xterm css custom colors file.

To test this, you can create a project with a commit like this: leipert/test-project@9e3b85fa

Go to the job page, you should be able to see this output: https://gitlab.com/leipert/test-project/-/jobs/86651121 The same should be valid if you try to write this data into the terminals in job and environments page: https://gitlab.com/leipert/test-project/-/jobs/86651121/raw

If you open any other page, on the dev tools, you should not see the xterm.css file.

What are the relevant issue numbers?

#44768 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #44768 (closed)