feat(secrets): add Doppler adapter

lib/kamal/secrets/adapters/doppler.rb

@@ -0,0 +1,28 @@
+class Kamal::Secrets::Adapters::Doppler < Kamal::Secrets::Adapters::Base
+  private
+    def login(account)
+      unless loggedin?(account)
+        `doppler login -y`
+        raise RuntimeError, "Failed to login to Doppler" unless $?.success?
+      end
+    end
+
+    def loggedin?(account)
+      `doppler me --json 2> /dev/null`
+      $?.success?
+    end
+
+    def fetch_secrets(secrets, account:, session:)
+      project, config = account.split("/")
+
+      raise RuntimeError, "Missing project or config from --acount=project/config option" unless project && config
+      raise RuntimeError, "Using --from option or FOLDER/SECRET is not supported by Doppler" if secrets.any?(/\//)
+
+      items = `doppler secrets get #{secrets.map(&:shellescape).join(" ")} --json -p #{project} -c #{config}`
+      raise RuntimeError, "Could not read #{secrets} from Doppler" unless $?.success?
+
+      items = JSON.parse(items)
+
+      items.transform_values { |value| value["computed"] }
+    end
+end