WIP: Extract artifacts upload into service

What does this MR do?

Introduce a service class Ci::UploadArtifactsService that takes all the complexity out of the Runner's POST /:id/artifacts API endpoint.

This moves some domain knowledge from the application layer down to the domain layer.

TODO

• write specs for service class
• write specs for new job.max_artifacts_size method

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

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