feat: metadata propagation through events

[jvillafanez]

Requires owncloud/reva#582

NOTE:

• "eventhistory" and "sse" services should be included for completion. However, they don't contact any other service, and there isn't anything worthy to report for tracing. At least the "eventhistory" needs access to the store, but we aren't tracing it at the moment and it will need refactoring.
• "antivirus" service uses a HTTP client. This might need to be rechecked because it might affect the propagation.

Known issue: #12281 (it should only affect to the tracing, the metadata propagation should work fine)

Description

Related Issue

• Fixes <issue_link>

Motivation and Context

How Has This Been Tested?

• test environment:
• test case 1:
• test case 2:
• ...

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[jvillafanez]

Need to double-check if we can remove this. The potential problem is if the context is canceled.
If we require the goroutine below to finish, we'll need a new context, but we'll need to move the metadata from one context to another.