[Redis 6.2] Add NOMKSTREAM option to XADD

[wmontgomery-splunk]

This adds the ability to add the NOMKSTREAM option to XADD. By default it does not add the option to the command, meaning that a stream will be created if it doesn't exist.

From the Redis documentation at: https://redis.io/commands/xadd/

Appends the specified stream entry to the stream at the specified key. If the key does not exist, as a side effect of running this command the key is created with a stream value. The creation of stream's key can be disabled with the NOMKSTREAM option.

References #978

[byroot]

Thank you!