fix: return 200 (not 202) for new synchronous endpoints (planning#460)

The endpoints and their respective response codes

                                      before              after
    1. PUT /v1/replies/<id>/reject -> 202                 200
    2. PUT /v1/replies/<id>/accept -> 202                 200
    3. PUT /v1/replies/<id>	       -> 202                 200
    4. PUT /v1/submission/<id>     -> 202                 202

returned a 202 in the positive case. This doesen't make sense since they're
synchronous requests and should return 200. For the not yet released new
endpoints 1, 2 and 3 we can still change that without breaking any kind of API
compatability.

For endpoint 4, we have to keep it at 202 for API compatability but add a marker
once v2 is considered.