Edge cache test site

Origin for validating POST /v1/edge-cache/purge by URL and by cache-tag.

/tagged/a - Cache-Tag: qs-tag-a
/tagged/b - Cache-Tag: qs-tag-b
/tagged/ab - Cache-Tag: qs-tag-a,qs-tag-b
/untagged - no Cache-Tag (control)
/custom/{tag1,tag2} - tags taken from the path