The PR adds support for the following flags on RedisModule_OpenKey:
* REDISMODULE_OPEN_KEY_NONOTIFY - Don't trigger keyspace event on key misses.
* REDISMODULE_OPEN_KEY_NOSTATS - Don't update keyspace hits/misses counters.
* REDISMODULE_OPEN_KEY_NOEXPIRE - Avoid deleting lazy expired keys.
* REDISMODULE_OPEN_KEY_NOEFFECTS - Avoid any effects from fetching the key
In addition, added `RM_GetOpenKeyModesAll`, which returns the mask of all
supported OpenKey modes. This allows the module to check, in runtime, which
OpenKey modes are supported by the current Redis instance.