Upgrade to Wagtail 7

[janbrasna]

One-line summary

This updates to use Wagtail 7.1.1 (the same as currently powering springfield)

Significant changes and points to review

These are the changes since last update work from Rob to LTS:
https://docs.wagtail.org/en/latest/releases/7.1.html

Issue / Bugzilla link

Closes #16334 as superseded.

Testing

yes please

not knowing too much about the internals I took it for a spin to see things work, and besides the usual images missing I hit all the content pages as:
http://localhost:8000/en-US/about/leadership/
http://localhost:8000/en-US/products/vpn/resource-center/
http://localhost:8000/en-US/products/vpn/resource-center/5-reasons-you-should-use-a-vpn/
http://localhost:8000/en-US/products/vpn/resource-center/what-is-a-vpn/
http://localhost:8000/en-US/products/vpn/resource-center/do-you-need-a-vpn-at-home-here-are-5-reasons-you-might/
http://localhost:8000/en-US/products/vpn/resource-center/what-does-a-vpn-do/
http://localhost:8000/en-US/products/monitor/
http://localhost:8000/en-US/products/monitor/what-is-a-data-broker/
http://localhost:8000/en-US/products/monitor/how-to-remove-your-information-from-the-internet/
etc. but please do take the CMS for a little spin to see nothing implodes with the models and types here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.68%. Comparing base (c5952ba) to head (08d8c94).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16820      +/-   ##
==========================================
- Coverage   79.69%   79.68%   -0.02%     
==========================================
  Files         159      159              
  Lines        8527     8525       -2     
==========================================
- Hits         6796     6793       -3     
- Misses       1731     1732       +1     

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[stevejalim]

besides the usual images missing

@janbrasna does https://mozmeao.github.io/platform-docs/cms/#ive-downloaded-a-fresh-db-and-the-images-are-missing help ?

[janbrasna]

Oh I think that one needs the worker running etc. and I've had way too much trouble even starting up with that mq/redis compose spec so I'm glad it's not run for me:)

(It probably just needs reading more docs.)

[janbrasna]

Also, I wanted to make a note here regarding #16534 that it's touching the josepy version here. In case that's something that needs to be watched in deployments, in case anything changes (and gets better locally or worse deployed).