The objective is to spike how fastly integration can be added, in relation to ezplatform-http-cache.

Expected deliverables as part of the spike:
1. Analyze if and how it would help to upgrade our fos-http-cache(-bundle) requirement to 2.x to implement this feature. According to the changelog, many of the changes are about tags and proxy clients (removed, as 2.x of fos-http-cache doesn't seem to be required for Fastly. See EZP-28065 for the dedicated story)
2. test the usage of the SURROGATE-KEY header used by Fastly, using the fos-http-cache tags configuration
3. prototype clearing cache on fastly using a fos-http-cache proxy client. This should come with the proxy configuration (fos-http-cache-bundle), as they exist for varnish, nginx, etc
4. (bonus) look into custom VCL and fastly, and try to determine if we will need one or not (might be too much for the scope of a spike)

With the result of the spike, we will decide if the prototyped elements are the way to go, or if we need to rethink the integration.