CacheableResponse should accept an array of header values

[Alexander Nestorov]

Welcome! Please use this template for reporting bugs or requesting features. For questions about using Workbox, the best place to ask is Stack Overflow, tagged with [workbox]: https://stackoverflow.com/questions/ask?tags=workbox

Library Affected:
_workbox-cacheable-response

Browser & Platform:
all browsers

Issue or Feature Request Description:
Currently, the CacheableResponse has two properties (statuses and headers), which can be used to cache responses conditionally. As per the example in the documentation:

const cacheable = new CacheableResponse({
  statuses: [0, 200],
  headers: {
    'X-Is-Cacheable': 'true',
  },
});

If the response is either 200 OR an opaque response and the headers contain a header named X-Is-Cacheable and the value of that header is true, then the response will be cached.

Note however that it's currently impossible to specify several values for the same header. E.g. I'd like to be able to do the following:

const cacheable = new CacheableResponse({
  statuses: [0, 200],
  headers: {
    'Content-type': ["image/webp", "image/png", "image/jpeg", "image/gif"],
  },
});