An administrator can update an animal

[emmeblm]

As an administrator
I want to update an animal's details
So that I can correct mistakes or change the details after I've created it

Acceptance criteria

Given an animal
When an administrator updates it (Http method PUT)
Then a 200 ok response is returned with the updated animal

Given an animal
When an administrator updates it (Http method PUT)
And an error occurs while updating it
Then a 503 service unavailable response is returned

Given an animal
When an administrator updates it (Http method PUT)
And the new animal is invalid
Then a 400 bad request response is returned with details of the invalid fields