Adding identity password settings to appsettings.json

[Aaron2404]

• Added identity password settings to appsettings.json
• Made the password validations and the messages in RegisterFormModelFluentValidator.cs synced with the settings instead of being hardcoded (before this was fine as it was not configurable anyway)
• Changed the names of the validation translations to short variable-like names instead of the entire English value which should make it look more clean.

[Bram1903]

Looks good!

@neozhu, this is a friend of mine, and because I'm not certain if this is what you want, you can merge it, or add changes as you like.

[neozhu]

@BoostioAaron I appreciate it a lot.