Add logging for Rails cache timeouts (#21667)

* Reduce redis cache store connect timeout from default 20 seconds to 5 seconds

* Log cache store errors

config/initializers/cache_logging.rb

@@ -0,0 +1,3 @@
+# Log cache errors with Rail's logger
+# This used to be the default in old Rails versions: https://github.com/rails/rails/commit/7fcf8590e788cef8b64cc266f75931c418902ca9#diff-f0748f0be8a653eea13369ebb1cadabcad71ede7cfaf20282447e64329817befL86
+Rails.cache.logger = Rails.logger

lib/mastodon/redis_config.rb

@@ -37,6 +37,7 @@ def setup_redis_env_url(prefix = nil, defaults = true)
   namespace: cache_namespace,
   pool_size: Sidekiq.server? ? Sidekiq.options[:concurrency] : Integer(ENV['MAX_THREADS'] || 5),
   pool_timeout: 5,
+  connect_timeout: 5,
 }.freeze
 
 REDIS_SIDEKIQ_PARAMS = {