[filebeat/input/redis/slowlog] Add client IP and name to documents

[jdheyburn]

Describe the enhancement:

The Redis SLOWLOG GET command responds back with fields for:

• Client IP address and port
• Client name if set via the CLIENT SETNAME command

https://redis.io/docs/latest/commands/slowlog-get/

Filebeat currently does not submit these.

Describe a specific use case for the enhancement or feature:

When viewing the slow logs in Kibana, we can use the client as another way to slice and dice visualisation to aid in where the slow commands are coming from.

[botelastic]

This issue doesn't have a Team:<team> label.