feat(cli): update secrets --account flag as optional depending on adapter

lib/kamal/secrets/adapters/test_optional_account.rb

@@ -0,0 +1,18 @@
+class Kamal::Secrets::Adapters::TestOptionalAccount < Kamal::Secrets::Adapters::Base
+  def requires_account?
+    false
+  end
+
+  private
+    def login(account)
+      true
+    end
+
+    def fetch_secrets(secrets, account:, session:)
+      secrets.to_h { |secret| [ secret, secret.reverse ] }
+    end
+
+    def check_dependencies!
+      # no op
+    end
+end