Feat [ Test ]: migrate from redis-mock to redis testcontainer for tests

[e11sy]

Since #326 we decided to set up redis testcontainer for tests instead of redis-mock lib
Also we needed to use new version of redis package (from 3.1.1 -> 4.7.0)

Problem

• Since we removed redis-mock we need to rewrite tests to new pattern
• Since we use new redis version we need to rewrite some of the redisClient calls
• Also we should use new redesClient calls in tests

Solution

• Set up redis testcontainer for tests
• Refactored Limiter and Grouper workers for them to be compatible with new redis version
• Refactored their tests
• Added initialize() and close() methods for RedisHelpers (now they are initialized and closed same as db in worker.start() and worker.finish())
• Now "redis": "^4.7.0" is root worker dependencie (since same version is used for tests)