MM-59934: Add Redis to CI and other improvements (#28164)

- Update library version.
- Added MaxFlush delay to help reduce CPU usage.
- Fall back to LRU cache for the caches which use SCAN.
- Added mattermost-redis and running for all api layer
tests in Postgres.

https://mattermost.atlassian.net/browse/MM-59934
```release-note
NONE
```

server/platform/services/cache/provider.go

@@ -82,6 +82,7 @@ type RedisOptions struct {
 	RedisAddr     string
 	RedisPassword string
 	RedisDB       int
+	DisableCache  bool
 }
 
 // NewProvider creates a new CacheProvider
@@ -91,8 +92,14 @@ func NewRedisProvider(opts *RedisOptions) (Provider, error) {
 		Password:          opts.RedisPassword,
 		SelectDB:          opts.RedisDB,
 		ForceSingleClient: true,
-		CacheSizeEachConn: 16 * (1 << 20), // 16MiB local cache size
-		//TODO: look into MaxFlushDelay
+		CacheSizeEachConn: 32 * (1 << 20), // 32MiB local cache size
+		DisableCache:      opts.DisableCache,
+		// This is used to collect more commands before flushing to Redis.
+		// This increases latency at the cost of lower CPU usage at Redis.
+		// It's a tradeoff we are willing to make because Redis is only
+		// meant to be used at very high scales. The docs suggest 20us,
+		// but going as high as 250us doesn't make any material difference.
+		MaxFlushDelay: 250 * time.Microsecond,
 	})
 	if err != nil {
 		return nil, err