What is the problem?
Before this change, the edit navigation menu tags modal was not
displaying tags that belonged to a tag_group when the tags_listed_by_group
site setting was set to true. This is because we are relying on the
/tags endpoint which returned tags in various keys depending on the
tags_listed_by_group site setting. When the site setting is set to
true, tags under belonging to tag groups were returned in the
extra.tag_groups attribute.
What is the fix?
This commit fixes it by pushing all tags in returned under the
`tag_groups` attribute into the list of tags to displayed. In a
following commit, we will move away from the `/tags` endpoint to a
dedicated route to handle the listing of tags in the modal.