Add publish-and-sync translations actions to editor and bulk workflows (Fixes #789)

[zanzo2003]

Solved Issue - #789
Summary

• introduce a shared sync_translation_source() helper and result dataclass so page/snippet updates, hooks, and actions reuse the same publish + machine-translation pipeline
• add a “Publish & sync translations” editor action that appears when translated copies exist, reusing Wagtail’s long-running button UX and posting the special submit value
• mplement a bulk “Publish & sync translations” action with confirmation template, permission checks, and descendant handling so editors can publish multiple pages and synchronize locales in one step
• expand regression coverage for the new button visibility, hook messaging/permissions, and bulk action behavior

[zanzo2003]

PFA Attaching test result