[FR] Add Feature flags (#4982)

* make currency choices independend

* Remove check for field, just try to get rid of it

* Add IF EXISTS to avoid error (works in postgres)

* Look for operational error, not programming error

* Use variants, depending on errors caused

* [FR] Add Feature flags
Fixes #4965

* Add option to define custom flags

* Revert "make currency choices independend"

This reverts commit ab84a7ff83.

* try fixing mysql

* more safeguards

* fix executioner call

* a fck

* use migrations. syntax

* and another round for mysql

* revert print change

* use UTC for datetime

* Update part.migrations.0112

- Add custom migration class which handles errors

* Add unit test for migration

- Ensure that the new fields are added to the model

* Update reference to PR

* fix ruleset for missing_models

* fix ruleset for flags_flagstate

* add API endpoints for flags

* add tests for new API endpoints

* fix tests

* fix merge

* fix tests

---------

Co-authored-by: martin <martin@iggland.com>
Co-authored-by: Oliver Walters <oliver.henry.walters@gmail.com>

requirements.txt

@@ -53,6 +53,7 @@ django==3.2.19
     #   django-dbbackup
     #   django-error-report
     #   django-filter
+    #   django-flags
     #   django-formtools
     #   django-ical
     #   django-import-export
@@ -92,6 +93,8 @@ django-error-report==0.2.0
     # via -r requirements.in
 django-filter==23.2
     # via -r requirements.in
+django-flags==5.0.12
+    # via -r requirements.in
 django-formtools==2.4.1
     # via -r requirements.in
 django-ical==1.9.1