Implement the newUiEnabled GraphQL resolving logic

What does this MR do and why?

Adds the necessary GraphQL changes for us to be able to interact with the newUiEnabled user setting.

References

This is part of a sequence of MRs that will eventually let us enable the new UI for all users on .com.

Step	MR
1. Create the necessary user setting in the DB	!211303 (merged)
➡️ 2. Create the necessary GraphQL resolvers	!211441 (merged) (this MR)
3. Leverage the new field in the product	!211301 (merged)

How to set up and validate locally

1. Run DB migrations.

2. Navigate to the GraphQL explorer: https://gdk.test:3443/-/graphql-explorer.

3. Run the following mutation to update the user setting:

   mutation setNewUIEnabled {
     userPreferencesUpdate(input: { newUiEnabled: true }) {
       userPreferences {
         newUiEnabled
       }
     }
   }

MR acceptance checklist

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