Add service classes for mutating AwardEmoji

What does this MR do?

EE backport https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15138.

This MR adds service classes to create, toggle and destroy AwardEmoji.

Adding, destroying and toggling emoji currently lack services and are instead performed through methods called on Awardable models.

This has led to inconsistencies where relevant todos are marked as done only when emoji are awarded through our controllers, but not through the API. Todos can also be marked as done when an emoji is removed, which doesn't seem correct!

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content
• [-] EE backport

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