Allow to specify read_path in datasource

[joelMuehlena]

When using the datasource to fetch data I can specify the path but not the getPath for the following readObject(). In my case this leads to an error, because the API expects a trailing slash and the {id} suffix is appended without a slash and the option to alter the used path.

E.g.

data "restapi_object" "user_admin" {
  path              = "/api/users/"
  query_string      = "username__iexact=admin"
  read_query_string = ""
  results_key       = "results"
  search_key        = "username"
  search_value      = "admin"
  debug             = true
}

throws an error because the provider tries a get to /api/users/{id} but should get from /api/users/{id}/.

Request:

Add the read_path attribute like it's done on the resource object.