Support disable ssl verify for etcd connection

[spacewander]

Currently when people want to connect etcd cluster via TLS, there is no way to disable SSL verify.

We need to solve it in two aspects:

1. allow disabling SSL verify in apisix/cli with luasocket
2. allow disabling SSL verify in lua-resty-etcd.

[spacewander]

This feature will solve #3225

[spacewander]

@starsz

[starsz]

Got it. Please assign it to me.

[tokers]

https://github.com/api7/lua-resty-etcd/blob/master/lib/resty/etcd/v3.lua#L113 @spacewander lua-resty-etcd already supports to verify SSL or not.

[spacewander]

But we don't pass the option to it.

[starsz]

Should lua-resty-etcd support blocking requests by using luasocket?
Then we can use lua-resty-etcd in apisix/cli.

[spacewander]

@starsz
It would be great. We can do it in a separate PR.

[tokers]

But we don't pass the option to it.

You mean APISIX or others?
https://github.com/apache/apisix/blob/master/apisix/core/config_etcd.lua#L502

[spacewander]

Sorry, it is my mistake...