Change release evidence creation status API from `202 Accepted` to `201 Created`
Spawned from the discussion here #211675 (comment 338189226)
Could we consider adding the id into the empty Evidence array, and then correcting the status code as a breaking change in 14.0?
Currently, we return
202 Accepted on
POST releases/:tag/evidence, not
Maybe we decided to do so because creation actually happens in the background job and it was logical.
But after #214819 it might be more logical to return 201.