Update users migration template to make email column case insensitive

[matthewmcgarvey]

With the addition of citext support in luckyframework/avram#608 it seems like a good idea to use it for user emails so that a person who makes an account with "MyAccount@example.com" can sign in with "myaccount@example.com" and no one else can make an account with the same email but with different capitalization.

lucky_cli/src/base_authentication_app_skeleton/db/migrations/00000000000001_create_users.cr

Lines 3 to 9 in 00cf926

	create table_for(User) do
	primary_key id : Int64
	add_timestamps
	add email : String, unique: true
	add encrypted_password : String
	end
	end

We would have to update the migration first to enable the citext extension and then add case_sensitive: false to the email line