Fix single Redis connection being used across all threads (#18135)

* Fix single Redis connection being used across all Sidekiq threads

* Fix tests

app/lib/redis_configuration.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+class RedisConfiguration
+  class << self
+    def with
+      pool.with { |redis| yield redis }
+    end
+
+    def pool
+      @pool ||= ConnectionPool.new(size: pool_size) { new.connection }
+    end
+
+    def pool_size
+      if Sidekiq.server?
+        Sidekiq.options[:concurrency]
+      else
+        ENV['MAX_THREADS'] || 5
+      end
+    end
+  end
+
+  def connection
+    if namespace?
+      Redis::Namespace.new(namespace, redis: raw_connection)
+    else
+      raw_connection
+    end
+  end
+
+  def namespace?
+    namespace.present?
+  end
+
+  def namespace
+    ENV.fetch('REDIS_NAMESPACE', nil)
+  end
+
+  def url
+    ENV['REDIS_URL']
+  end
+
+  private
+
+  def raw_connection
+    Redis.new(url: url, driver: :hiredis)
+  end
+end