bug: cannot use https when creating route through web UI

[mojerro]

Issue description

Environment

• apisix version (cmd: apisix version): 2.3
• OS (cmd: uname -a): Linux ecs-s2-large-2-linux-20190719115737 4.15.0-91-generic support PATCH for admin APIs #92-Ubuntu SMP Fri Feb 28 11:09:48 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
• OpenResty / Nginx version (cmd: nginx -V or openresty -V): nginx:1.18.0-alpine
• etcd version, if have (cmd: run curl http://127.0.0.1:9090/v1/server_info to get the info from server-info API): No
• apisix-dashboard version, if have: 2.4

Minimal test code / Steps to reproduce the issue

1. create a SSL certificate from browser
2. create an route an chose Enable HTTPS
3. click Next then throw the error

What's the actual result? (including assertion message & call stack if applicable)

What's the expected result?

It should go to the next step with out error

[tokers]

click Next then throw the error

@JoeyGaojingxing Could you provide the error details?

[spacewander]

Moved to apache/apisix-dashboard#1611