Better locale validation for unknown values

[robotdan]

Better locale validation for unknown values

Description

The Java Locale object is very permissive, and we do a bunch of validation today to ensure we have a properly formed country code, etc.

However, it is still possible to create a Locale object that passes various validation this is not correct. Review our current validation and further restrict the values that can be stored in user.preferredLanguages and registration.preferredLanguages.

Documentation

• Limit number of values to 20 for user or registration user.preferredLanguages and registration.preferredLanguages.

Community guidelines

All issues filed in this repository must abide by the FusionAuth community guidelines.

[robotdan]

Internal:

• https://github.com/FusionAuth/fusionauth-app/pull/277