Support SRV records in EE load balancer
Currently the EE load balancer code uses DNS A
records to discover hosts and assumes all of them are using the same port.
We'd like to add flexibility and add support for SRV
records so that we can provide both a hostname and a port. Consul supports this (https://www.consul.io/docs/agent/dns.html#service-lookups).
Related issue: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7651
/cc: @tkuah, @andrewn, @clefelhocz1