Set current Organization by header

What does this MR do and why?

Parse the X-GitLab-Organization-ID header as the current Organization. There is a frontend issue being worked on at the moment to send the header with requests.

References

Using the header as a current Organization input is defined at https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/organization/current_organization/#header-field

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Closes #548319 (closed)