copyurl: Add option to honor the HTTP header filename directive.

Implemented --header-filename for use with copyurl.

For specifically setting preferred download filenames for HTTP requests, RFC 6226
specifies a 'filename' directive, available within 'Content-Disposition'
header. We can handle with 'mime.ParseMediaType'.

See below for details:
https://httpwg.org/specs/rfc6266.html#disposition.parameter.filename
https://httpwg.org/specs/rfc6266.html#advice.generating

Co-authored-by: buengese <buengese@protonmail.com>

fs/operations/rc.go

@@ -274,8 +274,9 @@ func rcSingleCommand(ctx context.Context, in rc.Params, name string, noRemote bo
 		}
 		autoFilename, _ := in.GetBool("autoFilename")
 		noClobber, _ := in.GetBool("noClobber")
+		headerFilename, _ := in.GetBool("headerFilename")
 
-		_, err = CopyURL(ctx, f, remote, url, autoFilename, noClobber)
+		_, err = CopyURL(ctx, f, remote, url, autoFilename, headerFilename, noClobber)
 		return nil, err
 	case "uploadfile":