chore: deprecate Gateway.PathPrefixes

Context:
#7702 (comment)

cmd/ipfs/daemon.go

@@ -677,6 +677,10 @@ func serveHTTPGateway(req *cmds.Request, cctx *oldcmds.Context) (<-chan error, e
 		opts = append(opts, corehttp.RedirectOption("", cfg.Gateway.RootRedirect))
 	}
 
+	if len(cfg.Gateway.PathPrefixes) > 0 {
+		log.Error("Support for X-Ipfs-Gateway-Prefix and Gateway.PathPrefixes is deprecated and will be removed in the next release. Please comment on the issue if you're using this feature: https://github.com/ipfs/go-ipfs/issues/7702")
+	}
+
 	node, err := cctx.ConstructNode()
 	if err != nil {
 		return nil, fmt.Errorf("serveHTTPGateway: ConstructNode() failed: %s", err)

core/corehttp/gateway_handler.go

@@ -159,6 +159,7 @@ func (i *gatewayHandler) getOrHeadHandler(w http.ResponseWriter, r *http.Request
 	// If the gateway is behind a reverse proxy and mounted at a sub-path,
 	// the prefix header can be set to signal this sub-path.
 	// It will be prepended to links in directory listings and the index.html redirect.
+	// TODO: this feature is deprecated and will be removed  (https://github.com/ipfs/go-ipfs/issues/7702)
 	prefix := ""
 	if prfx := r.Header.Get("X-Ipfs-Gateway-Prefix"); len(prfx) > 0 {
 		for _, p := range i.config.PathPrefixes {

docs/config.md

@@ -559,6 +559,9 @@ Type: `bool`
 
 ### `Gateway.PathPrefixes`
 
+**DEPRECATED:** see [go-ipfs#7702](https://github.com/ipfs/go-ipfs/issues/7702)
+
+<!--
 Array of acceptable url paths that a client can specify in X-Ipfs-Path-Prefix
 header.
 
@@ -585,6 +588,8 @@ location /blog/ {
 }
 ```
 
+-->
+
 Default: `[]`
 
 Type: `array[string]`