feat: add notice to top of generated files

[dpilch]

Resolves #55

Add notice to the top of generated files warning users to not make modifications to
the generated files.

A sample generated file will look like this.

/***************************************************************************
 * The contents of this file were generated with Amplify Studio.           *
 * Please refrain from making any modifications to this file.              *
 * Any changes to this file will be overwritten when running amplify pull. *
 **************************************************************************/

/* eslint-disable */
import React from "react";
import {
  CustomButton,
  View,
  findChildOverrides,
  getOverrideProps,
} from "@aws-amplify/ui-react";
export default function BoxWithButton(props) {
  return (
    <View
      padding-left
      {...props}
      {...getOverrideProps(props.overrides, "View")}
    >
      <CustomButton
        color="#ff0000"
        width="20px"
        buttonText="Click Me"
        {...findChildOverrides(props.overrides, "CustomButton")}
      ></CustomButton>
    </View>
  );
}

The /* eslint-disable */ is included in the component text so that line has
been removed.

[johnpc]

lgtm!