public Content fromString(String text) {
      return fromStringWithRole(role, text);
    }
Creates a content from a string.

@param text a string which will be converted to a {@link com.google.cloud.vertexai.api.Part}
    with its text field set.
java-vertexai/google-cloud-vertexai/src/main/java/com/google/cloud/vertexai/generativeai/ContentMaker.java