Fix for unlisted_choice, docstring updates, and misc refactoring

[consideRatio]

Summary

• fixes #702 in 4c6e5df
• avoids a possible edge case issue in 4d2c754
• updates some docstrings and makes some smaller refactors

Review commit by commit!

I did quite a bit few changes, but they are grouped quite well by commit, which makes them quite easy to review. I've made a self-review commit by commit and made comments below.

• [x] 6fbbddb - refactor: move constant definition Trivial
• [x] 6cbea92 - Update docstrings and comments Only docstrings and comments
• [x] 50e6ed2 - refactor: de-nest _get_profile logic Very small, quick to conclude its just a safe refactor
• [x] 2871e97 - refactor: initialize a variable where its needed Trivial
• [x] 67bd9c4 - refactor: de-nest _populate_profile_list_defaults Very small, quick to conclude its just a safe refactor
• [x] 7d83813 - small fix: only make changes to a profile list copy Small fix, quite quick to review
• [x] 4d2c754 - refactor: rename and let profile_list helper function return a copy Very small, and quite quick to review
• [x] 81471a6 - Simplify development config and profile_list example Only development config and docs updated
• [x] facd52e - Add test for profile_list and profile_options mixup bug A test to reproduce bug fixed by the next commit
• [x] 4c6e5df - Fix mixing of profile slug and option slug Fixes #702

[consideRatio]

Thank you for the quick review @GeorgianaElena!!!

I'll go for a merge and rebase #774 based on the merge.