Added support for Allow Headers #492

[dpotkoc]

Closes #492

this is example from VCL file when CORS headers are enabled:
# Snippet edgemodule_cors_headers_deliver : 45 if (req.http.Origin && !resp.http.Access-Control-Allow-Origin && !resp.http.Access-Control-Allow-Methods && !resp.http.Access-Control-Allow-Headers) { if ( req.http.Origin ~ "^https?://google.hr" ) { set resp.http.Access-Control-Allow-Origin = req.http.origin; } set resp.http.Access-Control-Allow-Methods = "GET,HEAD,POST,OPTIONS"; set resp.http.Access-Control-Allow-Headers = "Content-Type,X-company"; set resp.http.Vary:Origin = ""; }

and configuration:

It is tested fetch from different domains and with different headers.