Switch workhorse go-redis client

What does this MR do and why?

This MR is a continuation of !128087 (merged) which implements keywatcher.go using a redis/go-redis client.

Use GITLAB_WORKHORSE_FF_GO_REDIS_ENABLED env variable to switch between implementations.

The main changes are

• CI changes
• goredis package
• changes to main
• exporting constants and metric counters in redis package by setting to public

Related to #413151 (closed)

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