config: new option config.etcd.http.request.interface

[TarantoolBot]

config.etcd.http.request.interface option is added in Tarantool 3.5.0.

It sets the interface to use as outgoing network interface for the etcd
configuration source.

The interface can be specified as an interface name, an IP address, or a
hostname.

See https://curl.se/libcurl/c/CURLOPT_INTERFACE.html for details.
Requested by @Totktonada in https://github.com/tarantool/tarantool-ee/commit/d329803e447cc15a688ccb2b5e73cb8af26157a4.