feat: Sort resource_group_labels by given order

[aifrak]

Let's say, we have this in a domain:

admin do
  show? true
  resource_group_labels group_b: "Group B", group_a: "Group A", group_c: "Group C"
end

Currently, resource_group_labels shows labels in ascending alphabetical order and this will result to this in the domain dropdown:

• Group A
• Group B
• Group C
• (resources without group)

This PR let resource_group_labels to strictly sort labels as given and this will be the result in the domain dropdown:

• Group B
• Group A
• Group C
• (resources without group)

The reason is that when I tried ash_admin with ash_paper_trail, I tried to group all resources with Version in a group called Audit log which starts with an A. There is another group called Domain. As result, Audit log group is always at the top and I wanted to actually put this group under the Domain group.

Follow up to #15

Contributor checklist

• Bug fixes include regression tests
• Features include unit/acceptance tests

[zachdaniel]

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