Generate gettext file for various error messages

[allenwyma]

Is your feature request related to a problem? Please describe.
Being able to translate error messages into different languages is quite important as most of the world speaks another language, natively.

Describe the solution you'd like
Generate a gettext file that can possibly be updated with a mix task, that will create a POT file so we can generate the translation for the error messages.

Maybe even for field names, we can also generate a "humanized" name.

Describe alternatives you've considered
Would need to manually create the file OR scan the deps of ash and generate the file.

Express the feature either with a change to resource syntax, or with a change to the resource interface

For example

 mix ash.codegen.gettext