chore: Add stackdriver exported metrics to Memorystore Redis SLIs

Furhan Shabirrequested to merge
chore/add-stackdriver-metrics-to-memorystore-redis-slis into master

What

Add stackdriver exported redis metrics to Memorystore SLIs to track redis primary server metrics.

Why

To provider more insight into primary_server health metrics for Memorystore Redis instances.

Reference issue: gitlab-com/gl-infra/tenant-scale/tenant-services/team#188 (closed)

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