WIP: Add jobs to categories

What does this MR do?

Shows the templates contained in the Jobs folder when selecting a gitlab-ci.yml template from the drop down.

This will aid the usability and reference-ability of composable auto devops.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated via https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26520
• Code review guidelines
• Merge request performance guidelines
• Style guides

Performance 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

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