Update package namespace settings permissions

🍭 What does this MR do and why?

Changes the required permissions to change namespace/group-level package settings from Developer to Maintainer.

This MR also refactors the permissions to use admin_package rather than have a separate subset of permissions for package settings. This is more aligned with the rest of the permissions throughout GitLab.

🍬 Screenshots or screen recordings

💻 How to set up and validate locally

1. Create a group (or pick an existing one)
2. Create a user
3. Add the user to the group as a Developer
4. While logged in as the Developer user, use the graphql explorer: http://gdk.test:3000/-/graphql-explorer to try to update the namespace package settings using the query below:

   mutation {
     updateNamespacePackageSettings(input: {
       namespacePath: "<your-namespace-full-path>", 
       genericDuplicatesAllowed:true, 
       genericDuplicateExceptionRegex: "asdf.*"
     }) {
       packageSettings {
   	 genericDuplicatesAllowed
         genericDuplicateExceptionRegex
       }
     }
   }

5. The request should be unsuccessful
6. Optionally, you can log back in as the root user or owner/maintainer of the group and make the request again, it should be successful.

📐 MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related: #350682 (closed)