Add Mastodon API service class, auth token config

Add a new REST API service class to keep things DRY

app/services/btcpay_manager_service.rb

@@ -1,7 +1,7 @@
 #
 # API Docs: https://docs.btcpayserver.org/API/Greenfield/v1/
 #
-class BtcpayManagerService < ApplicationService
+class BtcpayManagerService < RestApiService
   private
 
     def base_url
@@ -19,18 +19,4 @@ class BtcpayManagerService < ApplicationService
         "Authorization" => "token #{auth_token}"
       }
     end
-
-    def endpoint_url(path)
-      "#{base_url}/#{path.gsub(/^\//, '')}"
-    end
-
-    def get(path, params = {})
-      res = Faraday.get endpoint_url(path), params, 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