DRY up btcpay and lndhub services

Removing initialize methods from the main/manager class also allows for
different iniitalizers in specific task services

app/services/lndhub_v2.rb

@@ -1,13 +1,13 @@
 class LndhubV2 < Lndhub
 
-  def post(endpoint, payload, options={})
+  def post(path, payload, options={})
     headers = { "Content-Type" => "application/json" }
     if auth_token
       headers.merge!({ "Authorization" => "Bearer #{auth_token}" })
     elsif options[:admin_token]
       headers.merge!({ "Authorization" => "Bearer #{options[:admin_token]}" })
     end
-    res = Faraday.post "#{@base_url}/#{endpoint}", payload.to_json, headers
+    res = Faraday.post endpoint_url(path), payload.to_json, headers
     log_error(res) if res.status != 200
 
     JSON.parse(res.body)