Add synced unpublish, delete and move for pages

[zerolab]

This replaces #537 (and addresses #15)

https://github.com/wagtail/wagtail/pull/7984 / https://github.com/wagtail/wagtail/issues/7592

To run tests locally:

tox -e python3.8-django4.0-wagtailsync-sqlite wagtail_localize.tests.test_synctree.TestConstructSyncedPageTreeListHook

To-Do:

• [x] Decide what to do with multi-layered locale sync (fr-ca synchs from fr which syncs from en) -> YES
• [x] add a global setting to enable/disable this functionality (ref) -> let's make it a setting for opt-in
• [x] decide whether we support per-model overrides (ref) --> not to per model
• [ ] support multi-layered sync
• [ ] documentation

[codecov-commenter]

Codecov Report

Merging #551 (23b2d72) into main (7d6278c) will decrease coverage by 0.38%. The diff coverage is 4.16%.

@@            Coverage Diff             @@
##             main     #551      +/-   ##
==========================================
- Coverage   91.44%   91.06%   -0.39%     
==========================================
  Files          47       47              
  Lines        3894     3918      +24     
  Branches      591      601      +10     
==========================================
+ Hits         3561     3568       +7     
- Misses        192      207      +15     
- Partials      141      143       +2     

Impacted Files	Coverage Δ
wagtail_localize/wagtail_hooks.py	71.00% <4.16%> (-9.12%)	:arrow_down:
wagtail_localize/components.py	82.69% <0.00%> (-1.93%)	:arrow_down:
wagtail_localize/models.py	95.57% <0.00%> (-0.15%)	:arrow_down:
wagtail_localize/views/convert.py	71.62% <0.00%> (+1.35%)	:arrow_up:
wagtail_localize/views/edit_translation.py	85.44% <0.00%> (+1.53%)	:arrow_up:

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