[HOTFIX] Ensure returning the user body in the content property when serialized

[Aschen]

What does this PR do ?

Since the last release, the user content is accessible under the user._source property in addition to the user.content property.

A getter was added for backward compatibility but when a User object was returned in a controller action it was serialized with only the _source property, breaking existing APIs relying on the content property.

This PR fix that but the sent data will be duplicated. A safe serialize method has been added to the User, Role and Profile classes and should be used instead of returning the instances directly.

Other changes

Boyscout

[codecov]

Codecov Report

Merging #630 (c21faed) into master (8beec6a) will decrease coverage by 0.15%.
The diff coverage is 22.22%.

❗ Current head c21faed differs from pull request most recent head a8c2511. Consider uploading reports for the commit a8c2511 to get more accurate results

@@            Coverage Diff             @@
##           master     #630      +/-   ##
==========================================
- Coverage   86.30%   86.15%   -0.16%     
==========================================
  Files          34       34              
  Lines        1585     1589       +4     
  Branches      279      279              
==========================================
+ Hits         1368     1369       +1     
- Misses        159      162       +3     
  Partials       58       58              

Impacted Files	Coverage Δ
src/controllers/Document.ts	68.47% <0.00%> (ø)
src/core/security/Profile.ts	92.30% <0.00%> (-7.70%)	⬇️
src/core/security/Role.ts	62.50% <0.00%> (-8.93%)	⬇️
src/utils/Deprecation.ts	100.00% <ø> (ø)
src/core/security/User.ts	92.85% <66.66%> (-7.15%)	⬇️

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