Issue description

Will limit-req support nodelay and rate in minute?
If not, I find nodelay can be implemented by adding condition, but resty.limit.req only support rate in second, how can I implemnt rate in minute?

Environment

Request help without environment information will be ignored or closed.

• apisix version (cmd: apisix version): 2.5
• OS (cmd: uname -a): ubuntu
• OpenResty / Nginx version (cmd: nginx -V or openresty -V):
• 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):