Draft: feat(Conflict detection): #3589076 "Detect conflicts during auto-save polling"

The original branch with this work was merged in !1107 (merged) and reverted in !1205 (merged). In addition to the changes from 1107 this MR also now contains the commits from the !1199 (closed).

Original MR description is bellow

TL;DR: Adds HTTP 409 response to auto-save list endpoint when at least one "resolvable conflict" is detected.

For people with attention span or AI summary tools:

Ground work MR for "[META] Review of changes and Conflict resolution" #3587587. Adds "Detect conflicts during autosave polling" capability.

To keep the scope manageable, changes are limited to Page (canvas_page) entities. Effort is made to leave path open for other entity types.

List of changes:

• Expands src/Controller/ErrorCodesEnum.php by adding new error code 4 that is intended to distinguish HTTP 409 responses the UI will able to handle gracefully in !945
• Updates the error (#/components/schemas/Error) definition in openapi.yml by adding optional conflict_id property. On the BE we use Page revision id and cast it to string. String is used here as we plan to use a hash of property values for Config entities when we add support for those.
• Updates the auto-save entries list endpoint (/canvas/api/v0/auto-saves/pending) definition in openapi.yml by adding HTTP 409 response. This response returns body containing errors property that are described by updated the #/components/schemas/Error and also data that returns the auto-save entries as per HTTP 200 response. This allows client side to update the UI and inform the user about the detection of a conflict(s) and in future MRs provide the user with ways of resolving the detected conflict.
• Changes in AutoSaveManager, ApiAutoSaveController and ErrorCodesEnum to add functionality described above
• Minor refactor/quality of life improvements:
  • Moved some hardcoded auto-save properties that are not meant for client side from ApiAutoSaveController to AutoSaveManager::AUTO_SAVE_INTERNAL_PROPERTIES
  • Added new $with_conflicts argument to and made both arguments required (AutoSaveManager::getAllAutoSaveList(bool $with_entities = FALSE) to AutoSaveManager::getAllAutoSaveList(bool $with_entities, bool $with_conflicts)). Then updated usages of ::getAllAutoSaveList() to use updated method and added named parameters to invocations.
• Added temporary e2e fix to ui/tests/e2e/empty-canvas.cy.js that most likely can be removed in !945, commented that in !945 (comment 1069355).

Testing instructions

1. Create Page entity in Canvas, make a change, publish the changes
2. Modify same Page entity, but do not publish your changes, observe auto-save polling (HTTP GET to /canvas/api/v0/auto-saves/pending) respond with HTTP 200
3. Outside of Canvas resave the Page entity (using drush esav canvas_page <entity id> -y should work just fine)
4. Observe next Canvas auto-save poll (HTTP GET to /canvas/api/v0/auto-saves/pending) return HTTP 409:

   • Response should have errors and data properties

   • The data property should have all auto-save items as per HTTP 200 response

   • The errors property should have an entry for the Page entity modified in step 3.

   • The errors entry for the conflicting auto-save item must have property code with value 4 , identifying the HTTP 409 response as "resolvable in Canvas UI" as described in #3587587

   • The errors entry for the conflicting auto-save item

     must have meta property and it must contain conflict_id property set to string value of the current latest revision of Page entity (updated in step 3) that is stored in db

Closes #3589076