Maximum page size to 100 for API keyset pagination

This aligns with offset pagination, where we also allow up to 100
records max.

lib/gitlab/pagination/keyset/page.rb

@@ -5,9 +5,12 @@ module Gitlab
     module Keyset
       # A Page models the pagination information for a particular page of the collection
       class Page
-        # Default and maximum size of records for a page
+        # Default number of records for a page
         DEFAULT_PAGE_SIZE = 20
 
+        # Maximum number of records for a page
+        MAXIMUM_PAGE_SIZE = 100
+
         attr_accessor :lower_bounds, :end_reached
         attr_reader :order_by
 
@@ -22,7 +25,7 @@ module Gitlab
         def per_page
           return DEFAULT_PAGE_SIZE if @per_page <= 0
 
-          [@per_page, DEFAULT_PAGE_SIZE].min
+          [@per_page, MAXIMUM_PAGE_SIZE].min
         end
 
         # Determine whether this page indicates the end of the collection

spec/lib/gitlab/pagination/keyset/page_spec.rb

@@ -4,10 +4,10 @@ require 'spec_helper'
 
 describe Gitlab::Pagination::Keyset::Page do
   describe '#per_page' do
-    it 'limits to a maximum of 20 records per page' do
-      per_page = described_class.new(per_page: 21).per_page
+    it 'limits to a maximum of 100 records per page' do
+      per_page = described_class.new(per_page: 101).per_page
 
-      expect(per_page).to eq(described_class::DEFAULT_PAGE_SIZE)
+      expect(per_page).to eq(described_class::MAXIMUM_PAGE_SIZE)
     end
 
     it 'uses default value when given 0' do