Refactor trigger block and spec

What does this MR do?

The goal of this MR is to solve a wee little bit of technical debt in CI

• Use gitlab utility classes
• Use data-testid
• Use GlTable over native table element (also adds column headers key/value)
• Convert spec/frontend/jobs/components/trigger_block_spec.js to Vue test utils

Related to: #300693 (closed)

Where is this change at?

This change is in the Job sidebar of a job detail page. This change is visible if you have a trigger present on a job.

To test this change locally you can follow the docs here https://docs.gitlab.com/ee/ci/triggers/#making-use-of-trigger-variables

Screenshots (strongly suggested)

before	after

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