Feature: Add support for mem_total_replication_buffers redis 7.0 metric

[nantiferov]

Describe the problem

In Redis v7.0 #9166 added new metric mem_total_replication_buffers in INFO output for total memory of replication buffers used.

Checking metrics from latest exporter and code itself it looks like collecting of this metrics isn't supported atm. I can create PR with changes, since it looks like this metrics could be useful.

What version of redis_exporter are you running?
Please run redis_exporter --version if you're not sure what version you're running.

• 0.3x.x
• 1.x.x

Running the exporter
What's the full command you're using to run the exporter? (please remove passwords and other sensitive data)
Please include details about env variables, command line parameters, your orchestration setup, etc.

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Additional context
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