Issue description

I need to configure route which implement similar logic as this nginx config:

location ~ ^/foo/bar(/.*)? {
                return 302 $scheme://$host/app/bar$1$is_args$args;
}

But in redirect plugin I can only use $uri, which will contains /foo which I want to remove in the redirct locaton.

Environment

• apisix version (cmd: apisix version): 2.0
• OS (cmd: uname -a): Linux
• OpenResty / Nginx version (cmd: nginx -V or openresty -V): 1.19.3.1
• etcd version, if have (cmd: run curl http://127.0.0.1:9090/v1/server_info to get the info from server-info API):
• apisix-dashboard version, if have:
• luarocks version, if the issue is about installation (cmd: luarocks --version):