[redisreceiver] Fix metric types and units according to Redis semantics

[shmsr]

Description

• Changed metric types from Sum to Gauge for point-in-time measurements:
  • redis.clients.blocked - current count of clients pending on blocking calls
  • redis.clients.connected - current count of client connections
  • redis.rdb.changes_since_last_save - current count of changes since last dump
  • redis.slaves.connected - current count of connected replicas
  • redis.role - current role indicator
• Fixed units for replication offset metrics from "By" (bytes) to "1" (dimensionless):
  • redis.replication.backlog_first_byte_offset
  • redis.replication.offset
  • redis.replication.replica_offset
• Added legacy Redis role terminology to role attribute enum: master, slave, sentinel

Link to tracking issue

Fixes #40814

Testing

Documentation

[shmsr]

I added these based on the documentation: https://redis.io/docs/latest/commands/role/

Also, I took a INFO dump by connecting redis-cli to redis-server, I got this output:

# Replication
role:master

And master was not there in the enum. Also, added it to the last to maintain the enum order.

[shmsr]

@dmitryax / @hughesjj Did you get a chance to look at this?

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[atoulme]

@shmsr I am pinging the codeowners on slack - please review the conflict.

[dmitryax]

I don't see why the metrics have to be gauges. They are additive meaning if they are re-agregated, the values should be summed up. They seem to me proper UpDownCounters. See https://github.com/open-telemetry/opentelemetry-specification/blob/8aa1d27d9cf8c224299dcf0b58bfd5fcaacf88eb/specification/metrics/supplementary-guidelines.md#guidelines-for-instrumentation-library-authors for more details.

See #23454 for the second item. Looks like you're reverting it. We should avoid 1 units.

Please submit a separate PRs for each item where still applicable

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.