feat: Image Optimizer support

[TartanLlama]

Adds support for Image Optimizer with an added imageOptimizerOptions parameter for fetch.

Example usage:

import { Format, Orient, CropMode, Region } from 'fastly:image-optimizer';

addEventListener("fetch", (event) => event.respondWith(handleRequest(event)));

async function handleRequest(event) {
  return await fetch('https://www.w3.org/Graphics/PNG/text2.png', {
    imageOptimizerOptions: {
      region: Region.UsEast,
      format: Format.PNG,
      bgColor: {
        'r': 100,
        'g': 255,
        'b': 9,
        'a': 0.5
      },
      blur: '1%',
      brightness: -20,
      contrast: -20,
      height: 600,
      level: '4.0',
      orient: Orient.FlipVertical,
      saturation: 80,
      sharpen: { 'amount': 5, 'radius': 6, 'threshold': 44 },
      canvas: { 'size': { 'absolute': { 'width': 400, 'height': 400 } } },
      crop: { size: { absolute: { width: 200, height: 200 }, mode: CropMode.Safe } },
      trim: { top: 10, left: 10, right: 10, bottom: 10 },
      pad: { top: 30, left: 30, right: "1%", bottom: 30 }
    },
    backend: 'w3'
  });
}

Also upgrades Viceroy to version 15 in CI, as a more recent version is required for the stubbed IO hostcall.

Fixes #1194