Add schema validation and documentation for RemoteEvaluation

[MrSerth]

This PR contains two major changes, aiming to improve the robustness of usefulness of the remote evaluation:

• Add schema validation for RemoteEvaluation
• Add OpenAPI documentation for RemoteEvaluationController

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 69.52%. Comparing base (d99a715) to head (ad6d70a). Report is 24 commits behind head on master.

Files with missing lines	Patch %	Lines
app/models/runner.rb	33.33%	2 Missing :warning:
app/controllers/remote_evaluation_controller.rb	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2575 +/- ## ======================================= Coverage 69.52% 69.52% ======================================= Files 202 202 Lines 6360 6370 +10 ======================================= + Hits 4422 4429 +7 - Misses 1938 1941 +3 ```

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