Eager load http-cookie

We stumble upon https://gitlab.com/gitlab-org/gitlab/-/jobs/448781858 this as ~"master:flaky":

 ArgumentError:
  cookie store unavailable: :hash
# ./vendor/ruby/2.6.0/gems/http-cookie-1.0.3/lib/http/cookie_jar.rb:40:in `rescue in get_impl'
# ./vendor/ruby/2.6.0/gems/http-cookie-1.0.3/lib/http/cookie_jar.rb:37:in `get_impl'
# ./vendor/ruby/2.6.0/gems/http-cookie-1.0.3/lib/http/cookie_jar.rb:74:in `initialize'
# ./vendor/ruby/2.6.0/gems/rest-client-2.0.2/lib/restclient/request.rb:321:in `new'
# ./vendor/ruby/2.6.0/gems/rest-client-2.0.2/lib/restclient/request.rb:321:in `process_cookie_args!'
# ./vendor/ruby/2.6.0/gems/rest-client-2.0.2/lib/restclient/request.rb:75:in `initialize'
# ./vendor/ruby/2.6.0/gems/rest-client-2.0.2/lib/restclient/request.rb:52:in `new'
# ./vendor/ruby/2.6.0/gems/rest-client-2.0.2/lib/restclient/request.rb:52:in `execute'
# ./vendor/ruby/2.6.0/gems/rest-client-2.0.2/lib/restclient/resource.rb:51:in `get'
# ./vendor/ruby/2.6.0/gems/kubeclient-4.6.0/lib/kubeclient/common.rb:567:in `block in fetch_entities'
# ./vendor/ruby/2.6.0/gems/kubeclient-4.6.0/lib/kubeclient/common.rb:121:in `handle_exception'
# ./vendor/ruby/2.6.0/gems/kubeclient-4.6.0/lib/kubeclient/common.rb:567:in `fetch_entities'
# ./vendor/ruby/2.6.0/gems/kubeclient-4.6.0/lib/kubeclient/common.rb:554:in `load_entities'
# ./vendor/ruby/2.6.0/gems/kubeclient-4.6.0/lib/kubeclient/common.rb:134:in `discover'
# ./vendor/ruby/2.6.0/gems/kubeclient-4.6.0/lib/kubeclient/common.rb:465:in `proxy_url'
# ./app/models/clusters/applications/prometheus.rb:88:in `prometheus_client'
# ./app/models/concerns/prometheus_adapter.rb:28:in `can_query?'
# ./app/services/prometheus/proxy_service.rb:113:in `can_query?'
# ./app/services/prometheus/proxy_service.rb:67:in `execute'
# ./ee/app/controllers/ee/clusters/clusters_controller.rb:36:in `prometheus_proxy'

This seems to me a thread-safe issue, as I did recall this kind of error back in 2015: https://github.com/godfat/rest-core/commit/8b85837db400f29fc8df419a3b761ddd130ed581

That wasn't the most reliable fix, so I fixed it the other way in https://github.com/godfat/rest-core/commit/4ed06367675f2ecddf084abb51c00931d848de28

There were also various issues reporting this:

We need to somehow eager load it, otherwise this can jump out from time to time, and it would be difficult to investigate unless you hit into it in the past like me 😬