add Deployment, Environment, and ExternalIssue policies

app/policies/deployment_policy.rb

+class DeploymentPolicy < BasePolicy
+  def rules
+    delegate! @subject.project
+  end
+end

app/policies/environment_policy.rb

+class EnvironmentPolicy < BasePolicy
+  def rules
+    delegate! @subject.project
+  end
+end

app/policies/external_issue_policy.rb

+class ExternalIssuePolicy < BasePolicy
+  def rules
+    delegate! @subject.project
+  end
+end