Rework Devops Adoption API

What does this MR do?

This MR reworks DevopsAdoption API to work with new structure and store not only which groups should be calculated but also where exactly calculated data should be displayed.

Migration output

== 20210521073920 DropDevopsAdoptionNamespaceUniqueness: reverting ============
-- execute("DELETE FROM analytics_devops_adoption_segments WHERE id NOT IN (SELECT MIN(id) FROM analytics_devops_adoption_segments GROUP BY namespace_id)")
   -> 0.0037s
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:analytics_devops_adoption_segments, :namespace_id, {:name=>"index_analytics_devops_adoption_segments_on_namespace_id", :unique=>true, :algorithm=>:concurrently})
   -> 0.0068s
-- add_index(:analytics_devops_adoption_segments, :namespace_id, {:name=>"index_analytics_devops_adoption_segments_on_namespace_id", :unique=>true, :algorithm=>:concurrently})
   -> 0.0134s
-- transaction_open?()
   -> 0.0000s
-- indexes(:analytics_devops_adoption_segments)
   -> 0.0089s
-- remove_index(:analytics_devops_adoption_segments, {:algorithm=>:concurrently, :name=>"idx_analytics_devops_adoption_segments_on_namespace_id"})
   -> 0.0032s
== 20210521073920 DropDevopsAdoptionNamespaceUniqueness: reverted (0.0408s) ===

== 20210521073920 DropDevopsAdoptionNamespaceUniqueness: migrating ============
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:analytics_devops_adoption_segments, :namespace_id, {:name=>"idx_analytics_devops_adoption_segments_on_namespace_id", :algorithm=>:concurrently})
   -> 0.0127s
-- add_index(:analytics_devops_adoption_segments, :namespace_id, {:name=>"idx_analytics_devops_adoption_segments_on_namespace_id", :algorithm=>:concurrently})
   -> 0.0127s
-- transaction_open?()
   -> 0.0000s
-- indexes(:analytics_devops_adoption_segments)
   -> 0.0076s
-- remove_index(:analytics_devops_adoption_segments, {:algorithm=>:concurrently, :name=>"index_analytics_devops_adoption_segments_on_namespace_id"})
   -> 0.0038s
== 20210521073920 DropDevopsAdoptionNamespaceUniqueness: migrated (0.0431s) ===

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
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• I have self-reviewed this MR per code review guidelines.
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• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #329521 (closed)