Allow `max_artifact_size` to be changed via the REST API

What does this MR do and why?

Allow max_artifact_size to be changed via the REST API. This will be available for both Groups and Projects.

Note This will be only available for users who are admins

References

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• Ability to set maximum artifact size via API (#461906 - closed)

MR acceptance checklist

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Before	After

How to set up and validate locally

Note These instructions work for Projects, but changing the URL to http://gdk.test:3000/api/v4/groups/<group_id> should work the same

1. Create a Personal Access Token with the following scopes api, read_api, read_user, admin_mode for a user that has access to the admin area
2. Get the ID of the Project you want to change the max_artifacts_size attribute
3. Validate that you can read the new attribute when checking out the branch locally using

curl --header "PRIVATE-TOKEN: <token>" "http://gdk.test:3000/api/v4/projects/<project_id>"

This will return a JSON response, look for max_artifacts_size

{
  ...
  "warn_about_potentially_unwanted_characters":true,
  "autoclose_referenced_issues":true,
  "max_artifacts_size":null,
  "approvals_before_merge":0,
  "mirror":false,
}

4. Make a PUT request to update the Project

curl --request PUT --header "PRIVATE-TOKEN: <personal_access_token>" --url "http://gdk.test:3000/api/v4/projects/<project_id>" --data "max_artifacts_size=1"

Example response

{
  ...
  "warn_about_potentially_unwanted_characters":true,
  "autoclose_referenced_issues":true,
  "max_artifacts_size":1,
  "approvals_before_merge":0,
  "mirror":false,
}