WIP: CE Port: Web terminal from attached CI runner in Web IDE

What does this MR do?

Port of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7386

What are the relevant issue numbers?

Refs https://gitlab.com/gitlab-org/gitlab-ee/issues/5426

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