Fix job trace polling bug

What does this MR do?

1. Only starts fetching trace data when the job has started and has a trace.
2. Don't poll for data if visibility is hidden

How to test

• Pause your local runner and start a job (it should be in a pending state), check the network tab to ensure the trace endpoint is not called.
• Start a running job, switch to a new tab, switch back and ensure no trace endpoint calls were made while you were gone.
• Ensure everything with the job traces is still working as expected 🙏

Related to: #284103 (closed)

Screenshots (strongly suggested)

I wish I could but this is only code and network related ☹

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [ - ] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [ - ] Database guides
• [ - ] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team