redisreceiver: add metrics that are present in telegraf collector

[echlebek]

Component(s)

receiver/redis

Is your feature request related to a problem? Please describe.

Some users who are switching to the otel collector from telegraf have noticed that some of the metrics they relied on with the telegraf collector are unavailable.

Specifically, these are:
redis_keyspace_hitrate can be derived from existing metrics
redis_mem_fragmentation_bytes can be derived from existing metrics
redis_used_memory_overhead
redis_used_memory_startup
redis_tracking_total_keys
redis_cluster_enabled

I investigated each of these metrics and they are all made available by the redis INFO command, with the exception of redis_keyspace_hitrate which is a synthetic measure derived by computing redis_keyspace_hits / redis_keyspace_misses. (https://github.com/influxdata/telegraf/blob/master/plugins/inputs/redis/redis.go#L482)

Describe the solution you'd like

I'd like to propose that the above metrics, excluding redis_keyspace_hitrate and redis_mem_fragmentation_bytes, are added to the redisreceiver.

Describe alternatives you've considered

No response

Additional context

Telegraf documentation: https://github.com/influxdata/telegraf/tree/master/plugins/inputs/redis
Redis INFO documentation: https://redis.io/docs/latest/commands/info/

[github-actions]

Pinging code owners:

• receiver/redis: @dmitryax @hughesjj

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[VihasMakwana]

A discussion is already underway on the PR and it looks like a valid enhancement request.