fix(redis): Use a safer eviction rule (#3432)

Follow up to #3427 (comment)

redis.conf

@@ -14,13 +14,14 @@
 
 maxmemory 0
 
-# maxmemory-policy allkeys-lru
-#
 # This setting determines how Redis evicts keys when it reaches the memory limit.
-# 'allkeys-lru' evicts the least recently used keys from all keys stored in Redis,
+# `allkeys-lru` evicts the least recently used keys from all keys stored in Redis,
 # allowing frequently accessed data to remain in memory while older data is removed.
-#
-# Example:
-# maxmemory-policy allkeys-lru  # Use LRU eviction for all keys
+# That said we use `volatile-lru` as Redis is used both as a cache and processing
+# queue in self-hosted Sentry.
+# > The volatile-lru and volatile-random policies are mainly useful when you want to
+# > use a single Redis instance for both caching and for a set of persistent keys.
+# > However, you should consider running two separate Redis instances in a case like
+# > this, if possible.
 
-maxmemory-policy allkeys-lru
+maxmemory-policy volatile-lru