[FE] Group-level "DevOps Adoption" - Show data table for group

Let's reuse instance level code and implement the following changes on group level:

• Rename Add group button to add sub-group to table to be more specific
• Disable the Add group button when at the ultimate sub-group

Out of scope for this issue:

• Drilling down and up for a later iteration
• [DevOps Adoption] Add "This group" badge in adoption table

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