Resolve created_by and oncall_schedule n+1's in group member index

What does this MR do?

• Resolves user: :oncall_schedules n+1.
• Resolves :created_by n+1 in Groups::GroupMembersController#index
• Moves query analysis from serializer to controller spec with rendered views to catalog and analyze our performance/db query count.
• Modifies formatting of preload_all to match the includes formatting as described in Parameters. Same result, merely removing explicit mapping function from our code.

oncall schedules

What did this do before?

1. app/views/groups/group_members/index.html.haml calls group_members_list_data_attributes (in a few places).
2. Groups::GroupMembersHelper#group_members_list_data_attributes calls members_data_json.
3. Groups::GroupMembersHelper#members_data_json calls MemberSerializer.
4. MemberSerializer uses the MemberEntity.
5. MemberEntity exposes the user via MemberUserEntity.
6. ee version of MemberUserEntity exposes oncall_schedules, which uses the OncallScheduleEntity, which is then executed when invoked through the view in the first step causing our n+1.

created_by

What did this do before?

1. app/views/groups/group_members/index.html.haml calls group_members_list_data_attributes (in a few places).
2. Groups::GroupMembersHelper#group_members_list_data_attributes calls members_data_json.
3. Groups::GroupMembersHelper#members_data_json calls MemberSerializer.
4. MemberSerializer uses the MemberEntity.
5. MemberEntity exposes created_by, which is then executed when invoked through the view in the first step causing our n+1.

Performance analysis locally on GDK

Caveat This was done on a group where there were a handful of members(10), some of them being invited(45), and Access Requests(2). The numbers and query times will vary based upon size.

Before(after gdk restart and cache warm-up)

• ActiveRecord Query time: ~142ms
• queries(cached/uncached): 119

After(after gdk restart and cache warm-up)

• ActiveRecord Query time: ~80ms
• queries(cached/uncached): 56

Does this MR meet the acceptance criteria?

Conformity

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• Tested in all supported browsers
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Security

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• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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Related to #21033