When there is a timeout error with v1 API, return a more useful response to the user

Branches endpoint of API v1 sometimes time outs for repos with a very large number of branches and returns a 500 or 502 error.

It would be more useful to the user to get a JSON response with an explanation for the error, e.g.:
"Timeout, the request has taken longer than X seconds before sending any
data back, this could be because you have too many branches"