Add env vars

docs/services/etherpad/How it works.md

@@ -1,14 +1,22 @@
 # How it works
 
 ## Configuration
-- ETHERPAD_COOKIE__EXPIRES_SECONDS - time in seconds after which a session expires
-- ETHERPAD_ETHERPAD_COOKIE_RELEASE_THRESHOLD - time in seconds after which a session is not returned to the user
-- ETHERPAD_API_KEY - api key used for authentication of schulcloud server requests
-- ETHERPAD_URI - Used as base path for api client in nest
-- ETHERPAD__PAD_PATH - Used in legacy client to set path on cookie.
-- ETHERPAD__PAD_URI - Used for collab editor and lesson to build return url, Used in legacy client to build url
-- ETHERPAD__NEW_DOMAIN - Used in legacy client to validate url
-- ETHERPAD__OLD_DOMAIN -  Used in legacy client to validate url
+- FEATURE_ETHERPAD_ENABLED - Used to enable etherpad feature in feathers backend
+- FEATURE_COLUMN_BOARD_COLLABORATIVE_TEXT_EDITOR_ENABLED - Enables etherpad feature on column boards
+
+- ETHERPAD_COOKIE_EXPIRES_SECONDS - Time in seconds after which a session expires
+- ETHERPAD_ETHERPAD_COOKIE_RELEASE_THRESHOLD - Time in seconds after which a session is not returned to the user
+
+- ETHERPAD_API_KEY - Api key used for authentication of schulcloud server requests
+
+- ETHERPAD_URI - Uri of etherpad api for all calls like create, delete etc. Used as base path for api client in nest and feathers backend.
+
+- ETHERPAD__PAD_URI - URI to etherpad client api. Used in backend in collaborative text editor and lesson to build return url. Used in legacy client to build url.
+- ETHERPAD_OLD_PAD_URI - Used in feathers backend to restrict access to old etherpad urls to lesson context. Only defined in default.schema.json and not in dof-app-deploy 
+- ETHERPAD__PAD_PATH - Path to etherpad client api. Used in legacy client to set path on cookie.
+
+- ETHERPAD__NEW_DOMAIN - Etherpad Domain. Used in legacy client to validate url
+- ETHERPAD__OLD_DOMAIN - Old Etherpad Domain. Used in legacy client to identify old urls in lessons and transform them to urls with new domain.
 
 ## Creating and Opening an Etherpad Element on a Column Board