Moving file response functionality to shared folder (#22226)

* Moving file response functionality to shared folder

* Linter fixes

* Added the attachment serve to shared folder

* Removed the unwanted logs

* import fixes

* Linter fixes

* License added

* Moved UnsafeContentTypes and MediaContentTypes from api4

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

api4/cloud.go

@@ -14,6 +14,7 @@ import (
 	"github.com/mattermost/mattermost-server/v6/audit"
 	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+	"github.com/mattermost/mattermost-server/v6/shared/web"
 )
 
 func (api *API) InitCloud() {
@@ -647,7 +648,7 @@ func getSubscriptionInvoicePDF(c *Context, w http.ResponseWriter, r *http.Reques
 		return
 	}
 
-	writeFileResponse(
+	web.WriteFileResponse(
 		filename,
 		"application/pdf",
 		int64(binary.Size(pdfData)),