Propagate client identity to gitaly

What does this MR do?

This patch implements propagation of username and remote_ip to gitaly.

The goal of this is to make gitaly client-aware. The primary use case for this is logging. As SREs for gitlab.com, we frequently need to diagnose an increase in traffic and/or latency. Without having this information in the gitaly logs, it requires manually following correlation_ids to other logs, which is often very error prone. By including the client identity in the gitaly logs, we can tell right away which clients (logged in or anonymous) are generating traffic.

The gitaly-side support for this was merged in gitaly!2802 (merged), and these parameters are already being sent from gitlab-shell: gitlab-shell!436 (merged).

Screenshots (strongly suggested)

n/a

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

refs #232645 (closed)