Make ftl call automatically work with HTTP ingress endpoints

[alecthomas]

HTTP ingress verbs have the signature verb(builtin.HttpRequest<T>) builtin.HttpResponse<T, E>, which makes them quite irritating to call with ftl call. ftl call could either automatically detect these verbs and generate the wrapping HttpRequest, or allow curl-like flags to be defined which would perform this wrapping if used.

eg.

ftl call --POST foo '{...}'

Would automatically create the HttpRequest envelope {method: "POST", body: {...}}.