post/put/patch methods must specify all headers if present in options passed to method

[joeldodge79]

LookerSDK.client. merge_content_type_if_body fails to delete options[:headers] (as for instance LookerSDK.client.parse_query_and_convenience_headers correctly does) so the caller must supply content_type in order for the call to work.

E.g I'd expect the following to pass both "my-header" and "content_type" headers to the server:

sdk.create_some_resource(
  {resource_name: "foo", an_attr: "bar"},
  {headers: {"my-header" => "something"}},
)

instead it only passes "my-header" and so the caller must do the following to get it to work:

sdk.create_some_resource(
  {resource_name: "foo", an_attr: "bar"},
  {headers: {content_type: "application/json", "my-header" => "something"}},
)