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/btcpay_manager_service.rb

@@ -2,23 +2,35 @@
 # API Docs: https://docs.btcpayserver.org/API/Greenfield/v1/
 #
 class BtcpayManagerService < ApplicationService
-  attr_reader :base_url, :store_id, :auth_token
-
-  def initialize
-    @base_url   = Setting.btcpay_api_url
-    @store_id   = Setting.btcpay_store_id
-    @auth_token = Setting.btcpay_auth_token
-  end
-
   private
 
-    def get(endpoint)
-      res = Faraday.get("#{base_url}/#{endpoint}", {}, {
+    def base_url
+      @base_url ||= "#{Setting.btcpay_api_url}/stores/#{Setting.btcpay_store_id}"
+    end
+
+    def auth_token
+      @auth_token ||= Setting.btcpay_auth_token
+    end
+
+    def headers
+      {
         "Content-Type" => "application/json",
         "Accept" => "application/json",
         "Authorization" => "token #{auth_token}"
-      })
+      }
+    end
 
+    def endpoint_url(path)
+      "#{base_url}/#{path.gsub(/^\//, '')}"
+    end
+
+    def get(path)
+      res = Faraday.get endpoint_url(path), {}, headers
+      JSON.parse(res.body)
+    end
+
+    def post(path, payload)
+      res = Faraday.post endpoint_url(path), payload.to_json, headers
       JSON.parse(res.body)
     end
 end