Implement task matcher endpoint

[begedin]

Problem

In addition to #736, we would require an endpoint which calls the described module and returns the results. It would require authentication, but not authorization.

The ember side would need to have a service module which would access this endpoint. There are multiple ways we could likely achieve it, but that's something to discuss in the related ember issue.

Subtasks

• Add described endpoint - endpoint should receive a user id and return a list of matched tasks. It can probably go into `/tasks/for-user/
• Endpoint should require authentication, but it's safe enough not to require any authorization
• Add tests for endpoint

References

• related to Feature Checklist: Matching users with tasks #668, Implement basic task matcher module #736
• blocked by Implement basic task matcher module #736