PERF: Use Redis SET EX GET instead of LUA script for counting (#15939)

This will prevent Discourse from booting on Redis < 6.2.0

config/initializers/001-redis.rb

@@ -8,3 +8,8 @@ end
 # Pending https://github.com/MiniProfiler/rack-mini-profiler/pull/450 and
 # upgrade to Sidekiq 6.1
 Redis.exists_returns_integer = true
+
+if Gem::Version.new(Discourse.redis.info['redis_version']) < Gem::Version.new("6.2.0")
+  STDERR.puts "Discourse requires Redis 6.2.0 or up"
+  exit 1
+end