[Backport]Autocomplete: Change user authorization to use terms query for projects

What does this MR do and why?

(cherry picked from commit db392509)

Description from original MR Autocomplete: Change user authorization to use ... (!187862 - merged)

Update the Elasticsearch query used for filtering users during autocomplete to prevent too_many_clauses errors as reported in #534033 (closed). This is seen when the current user has many authorized groups or projects.

The change combines all the ids for authorized projects into one terms query instead of having one prefix query per project, thereby reducing the number of clauses.

Before

{:query=>
  {:bool=>
    {:must=>[{:simple_query_string=>{:_name=>"user:match:search_terms", :fields=>["name", "username", "public_email"], :query=>"maddiev~", :lenient=>true, :default_operator=>:and}}],
     :should=>[],
     :filter=>
      [{:term=>{:type=>{:_name=>"doc:is_a:user", :value=>"user"}}},
       {:term=>{:in_forbidden_state=>{:value=>false, :_name=>"filter:not_forbidden_state"}}},
       {:bool=>
         {:should=>
           [{:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>22}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>24}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>27}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>29}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>"1-p15-"}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>"31-p6-"}}}],
          :minimum_should_match=>1}}]}},
 :highlight=>{:fields=>{:name=>{}, :username=>{}, :public_email=>{}}, :number_of_fragments=>0, :pre_tags=>["gitlabelasticsearch→"], :post_tags=>["←gitlabelasticsearch"]}}

After

{:query=>
  {:bool=>
    {:must=>[{:simple_query_string=>{:_name=>"user:match:search_terms", :fields=>["name", "username", "public_email"], :query=>"maddiev~", :lenient=>true, :default_operator=>:and}}],
     :should=>[],
     :filter=>
      [{:term=>{:type=>{:_name=>"doc:is_a:user", :value=>"user"}}},
       {:term=>{:in_forbidden_state=>{:value=>false, :_name=>"filter:not_forbidden_state"}}},
       {:bool=>
         {:minimum_should_match=>1,
          :should=>
           [{:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>22}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>24}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>27}}},
            {:prefix=>{:namespace_ancestry_ids=>{:_name=>"namespace:ancestry_filter:descendants", :value=>29}}},
            {:terms=>{:namespace_ancestry_ids=>["1-p15-", "31-p6-"], :_name=>"namespace:ancestry_filter:project_ids"}}]}}]}},
 :highlight=>{:fields=>{:name=>{}, :username=>{}, :public_email=>{}}, :number_of_fragments=>0, :pre_tags=>["gitlabelasticsearch→"], :post_tags=>["←gitlabelasticsearch"]}}

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
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• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.

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