Draft: Switch to go-redis client

What does this MR do and why?

This MR replaces gomodule/redigo with redis/go-redis.

Addresses #413151 (closed)

Some notable areas of change

• Retained all files in internal/redis. Minor adjustments to WatchKey method signature and make a bunch of constants/variables public for re-use.
• Added code into internal/goredis, retaining at keywatcher's logic and tests
• updated main.go to switch between goredis. NewKeyWatcher and redis. NewKeyWatcher via GITLAB_WORKHORSE_FF_GO_REDIS_ENABLED envvar

Points to note on goredis implementation:

• no more dialers, instead go-redis internal handles dialing
  • note that connections in Pubsub are not part of the Client's pool (the restriction byPoolSize applies only when running commands on redis.Client, e.g. GET commands)
• running specs against a Redis instance in CI via config.toml (#413151 (comment 1478866105))

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