Support/wagtail 42 upgrade

[nickmoreton]

This upgrade wagtail to v4.2

Support ticket: 1166257309

Some of the changes here are not specifically for this upgrade and look like they are items form either version upgrades that were missed.

• Imports and use_json_field + some migrations
• wagtail_redirect_importer (removed as it's now part of wagtail since 2.10)

Additionally:

• Check Student page inline javascript still works as expected. 8bcefd4

[codecov-commenter]

Codecov Report

Merging #936 (b20f800) into master (d73ea18) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #936      +/-   ##
==========================================
- Coverage   52.99%   52.97%   -0.02%     
==========================================
  Files         161      161              
  Lines        7688     7686       -2     
  Branches      164      164              
==========================================
- Hits         4074     4072       -2     
  Misses       3497     3497              
  Partials      117      117              

Files Changed	Coverage Δ
rca/programmes/models.py	73.15% <ø> (ø)
rca/projects/models.py	47.86% <ø> (-0.25%)	⬇️
rca/settings/base.py	62.96% <ø> (ø)
rca/shortcourses/models.py	86.77% <100.00%> (-0.11%)	⬇️

[alxbridge]

@nickmoreton These changes all look good, and are complete as far as I can see. I've also done some testing of the site functionality, though I've not checked all the critical paths from the upgrading doc.

praise Thanks also for catching and addressing the changes which were still needed from previous upgrades.